You're probably doing the right thing by stepping in. Unless you're familiar with the other dog and can trust that it won't up the ante (and trust your own dog to keep it short and noisy, with no blood), the chances of it escalating are not worth the risk. Especially in a dog park, where other dogs are prone to jumping in on a fight, things can get out of hand too quickly. Additionally, dogs that don't read those kinds of very clear shut off signals (retreating to a bench and sitting down are pretty clear) are pretty likely to be the kinds of dogs that aren't going to take her corrections seriously, and instead try to play roughly with her which could push her to bite. Alternatively, they may take the correction as a significant threat and respond by turning it into a real fight. Either way, it's no good for you or your pup. I'm generally a big fan of proactive dog ownership, and I have, can, and do pick my own pup up (she's 65 lbs) and leave an area if a dog is bullying her and I can't safely leave her on the ground to have her run away with me. Hope that helps!