Daughter's Bad Habit

Itching on the bottom can be caused by parasites. You could ask your doctor how to cure it or go to a naturopath who could help with a parasite cleanse. Good luck!

OK, so I'm daring to head in a different direction here... Are you sure she is rubbing because it itches? Your discription is that she is rubbing her bottom. Does this mean she is bending over and rubbing her bottom on things or is she straddeling and rubbing? Because I would assume that during the time she had the UTI she may have discovered that the rubbing (assuming it is in a straddle) felt good.
If this is the case, don't freak out because it's normal. In fact a friend of mine had this same thing with her own daughter. My friend got advice from somewhere (I don't recall if it was an article, book, therepist or doctor) that the best thing to do is simply ignore it or tell her that it should be done in private like going to the bathroom or blowing your nose is done.
Of course I'm making some assumtions here based on a lack of a good description of how she is rubbing. LOL.

You might also try some children's probiotics and NutriBiotic's Grapefruit Seed Extract. My daughter has had a few infections and she has exzema. Both things are good preventatives. For the itchy skin for my daughter, I use Eucerin Calming Creme. I've tried a lot of stuff on her, including things the allergist and pediatrician recommended, but this is the only lotion that absolutely stops the itching within 24 hours. So now we apply it twice daily. If we miss even one time, the itching returns.

First thought is she needs less sugar and more yogurt - every day. And not the sugary yogurt - buy plain WHOLE fat yogurt and add honey or maple syrup (a little), with fruit at home.
My 2cents,
-B.