It's important to know that there are several different types of places to eat in Paris. A place called a "restaurant" is generally for formal, high-end dining with multiple courses. Restaurants also have specific lunch and dinner hours. I found that the best bet for good food at reasonable prices were the "brasseries", which are relatively informal and serve at all hours. Specialty places like creperies and ethnic restaurants also provide good options.

Avoid the cluster of restaurants around Saint Severin. They're not very good and cater to drunk tourists who come to Paris to party. There are more isolated restaurants just a few blocks away can be very good.

I really, really, liked the Musee d'Orsay. It was easier to get into than the Louvre and had some beautiful art, including a room of Van Goghs.

Check out the street performers in front of the Jeu de Paume.

Walk around the city, if your mother is up to it.

Check out Rick Steves's web site (and store in Edmunds, WA). He has great advice about attitude, packing light, and keeping your stuff from getting stolen.

Stay somewhere very central so you can walk most places. You can find decent prices if you search. Great walking city. I like to stay near the Pont Neuf on the right bank or just off Place de la Madeleine. I don't like Opera/grands magasins, way too crowded. Place de la Madeleine is home to great food shops and you'll find Laduree (should be an accent over the 1st e) there, a wonderful tea room - pastry shop that's a must-visit. I prefer to skip the somewhat stale rolls most hotels offer for breakfast, and go straight there. Ile St-Louis is a must-visit, especially twilight, and home to the famous ice-cream shop Berthillon - tiny scoop of ice cream on a cone, don't expect American portions! but delicious, agenaise is my favorite. You'll find fair restaurants nearby on the Ile. Check the concert schedules; you might be lucky enough to hear something at la Sainte-Chapelle on the Ile de la Cite (again, sorry for lack of accent marks) - which is something you must see in any case - http://en.wikipedia.org/wiki/File:Sainte_Chapelle_-_Upper_level_1.jpg - along with Notre Dame.
The Eiffel Tower is worth the time.
And Galleries Lafayette, the big dept store, fabulous, for its architecture as well as its wares.

Ditto on the fashion. Stay comfortable, of course, but try to bring dressier, more put-together pieces. Suggestions:

- Blazer. Easy to throw over casual outfits.
- A pretty, thin scarf that you can wear around your neck and also roll out to be a shawl. Uber practical, and scarves are de rigeur for French women.
- Flat dress boots, if you've got them. Another easy way to fancy up an outfit, but good for travel.

Think classic lines and pieces.

Otherwise, it's been a loooong time, and I was only in Paris for three days on a school trip.

1. Don't miss the Musee D'Orsay. It's a former train station, but fabulously converted. It's light, airy, clean, and chock full of beautiful art. Top Impressionist and Post-Impressionist collections.

2. Don't take any boat tours along the Seine. The one we went on was arduously slow, and the tour was given in FOUR languages at once. Ugh.

3. Macaroons! http://www.laduree.fr/v1/index.htm

Stay in an apartment instead of a hotel. We stayed in a one-bedroom about a block from the Louvre and it was awesome. Never actually went into the Louvre, but the location was fantastic.

Go to Notre Dame and do both the walking around inside and the climb to the top. You'll hate me for that advice halfway up the stairs, but it's unbelievably worth it once you reach the top.

I disagree about the boat tour. You should do it. It's a nice break from all the walking you'll be doing, not very expensive and probably something your mom will enjoy.

You should really have boeuf bourgignon while you're there. Check out the menus on the outside of restaurants in the St. Germain and go in if it's on the menu. It's TO DIE and you can't hardly find it in Seattle. Unless you're a vegetarian, then ignore that advice.

And basically eat as many desserts and breads as you can stomach, because once you come back, your American palette will be ruined for months (in a good way).

This is a TOTALLY biased answer so take it with an appropriate grain of salt, but a longtime friend of mine is a travel writer and American ex-pat to France (today is actually the day she gets her dual citizenship!) and she writes a blog and newsletter called Secrets of Paris, which is focused on good, often off-the-beaten-track stuff for both the American traveler and ex-pat. You might check out her site for some ideas - there are free resource guides at the bottom of her main page. 

End of plug!

And from my own trips there, I have to say that while sitting in a cafe and people watching seems terribly cliched, it is still awesome. I also agree with Cedarthvader on dress; you'll feel more comfortable out and about if you are more put-together than one might typically be in the States.

I hope you have a great time!

I really enjoyed the Conciergerie (the prison where Marie Antionette was held before being beheaded), the Paris Sewer Tour, the Holocaust Memorial/Deportation Point (it's right by Notre Dame, also a must-see), and a side trip to Versailles was AMAZING.

So much of the fun of Paris, though, is just wandering around, looking at the amazing shops (chocolate shaped like purses! Handmade marionettes!), popping in Boulangeries for croissants, goggling at food stalls with pig heads and tiny birds, and taking in the fashion. Have fun! And bring the absolute best clothes you own or you will feel dumpy.

Good advice all around. I'll add a couple, all in Paris:

Walk around Montmartre, the hillside surrounding the beautiful Sacre Coeur church in north Paris.

In addition to Galeries Lafayette, you should go into the nearby Printemps (another grand department store) and have a cup of tea or coffee in the tearoom, top floor, under the amazing stained glass ceiling.

The most wonderful of the pure touristy things to see is the Eiffel Tower, which is more gorgeous than you expect. You don't have to go up it; just walk around the grounds.

Go to the Jardin du Luxembourg (a large park in the middle of Paris, on the left bank) and wend your way to the pond in the middle. Watch the boys tend their toy boats with sticks. You will be charmed, and it's a great place to relax if you're walked out. All around the park is fantastic people-watching.

Also: don't call it "chunnel". English people get really snippy and annoyed when you do. Call it "Eurostar".

Don't swim over there. You should probably, like, take a plane or something.

If you'r on the budget, learn the metro. It's easy when you get the hang of it and can get you off the beaten path.
Which leads me to: stay in an outer neighbourhood to get a different feel and save money. There's this one neighbourhood I discovered a long time ago that was right next to an amazing cheese market, rows of hostels/hotels with cute private rooms for 10 euros. Not to mention it was a nearly 5 minute metro trip to downtown.
Stop every couple hours at a cafe during your day. Sit oustside, watch locals do there errands, gossip, etc. Fun.
Learn at least minimal French. Iv'e always got the feeling that the French typically are offended when you assume/demmand that they speak english. "trying" even if your French is truly pathetic is a nice gesture I think, and rude locals can easily ruin your day.
Go to the Eifell tower at night. Magical!
If you go to restaurant, understand that you are entering into a timeless zone where the waiters dictate when you recieve your food, check etc.
Also an "entree" In France means an appetizer, not a main meal.
You will walk Everywhere! Bring confortable shoes, but if you wear sneakers you will stand out like a sore thumb.

Sights that I enjoyed: The Musée d'Orsay. The Ste. Chapelle. The building of the Grande Arche de la Défense. The building of the Institut du Monde Arabe. The Bois de Vincennes. The Musée Georges Pompidou. The bottom of the Eiffel Tower.

Sights that I didn't enjoy as much: Arc de Triomphe, Place de la Concorde, spending what felt like an entire day in the Louvre, Invalides, Panthéon, L'Opéra.

Cheeses that are worth eating: brique de chêvre, roquefort papillon, St. Nectaire, Reblochon, any fresh goat cheese, herbed or not, Rocamadour...

Things that are significantly more available at grocery stores there, which are also delicious: terrines of various kinds. Cider from Normandy.

How to get your bread at the bakery: not too crispy. ("pas trop cuit" - [patʁoky'i]).

Daytrips that are worth making: There are probably many. But, one that is both easy and worthwhile is going to Rheims. Easy because there is a hi-speed train that goes there. Worthwhile because of the Cathedral, the basilica, and the champagne.

What everyone else said that is true: Dress nicely. Walk around. Watch people. Drink wine. Eat charcuterie.