You may want to try a 100% water change. In a tank 1-3 gals unfiltered, 1 50% and 1 100% water change with water conditioner per week is what your goal is. Not for "dirty" water, but for what you can't see, ammonia/nitrate/ites that build up in smaller tanks. She may be suffering one of those poisonings. She could of been fine all this time with it, but all it takes is a lower immunity, a little sick, age, something and it will get to them.
Seeing the moving worm started up her instinct and that is why she went after it.. I'm still stumped as to why she isn't eating. There is very few diseases and illnesses that has loss of appetite as one of the top 3 symptoms.. Cotton mouth, Hole in the Head, fin rot and ich are the usual suspects. If there are no other symptoms that you see other then lethargy (all those have lethargy associated with them too), there may be something internal going on that we just don't see.
Is her belly swollen? Does she have white spots on her that look like grains of salt? How are her fins?
I'm sorry, I wish I could help more, but the loss of appetite stumps me =(