The vet called yesterday, and said that it was just an infection, probably from a thorn or some other object that got stuck in her lip. the results showed that there were just a lot of white blood cells. The vet said that we can give antibiotics if we want (no way!), but I said that it had gotten smaller. She asked, "Is it 80% smaller?" and yes, it is at least 80% smaller. So, she said that if it comes back they can remove it, but it's fine for now.
So relieved!
Thanks for the support!