A dear teacher friend of mine says that "for every one day we change our routine, it takes about three to change it back".
My little guy has a *really* hard time with antibiotics.(So do I, for that matter, so I have some empathy.) If you can, serve her what she wants to eat--within reason of course, and add powdered probiotics to it. My son loved applesauce and yogurt. Perhaps a soy yogurt would be a nice substitute for pudding. It sounds like she's craving stomach comfort food.
You can also offer a lightly steeped licorice tea, which is soothing, for her to sip. When she's three or older, you can make a paste out of a 1/4 teaspoon of powdered slippery elm, or sprinkle it on some applesauce. This is a very effective remedy as slippery elm soothes the mucous membranes of the throat, stomach and intestines. Avoid milk, dairy and proteins for a few days. Our son wanted mostly crackers and brothy foods. I made mild soups of celery, carrots and noodles with a veggie broth, and he'd eat mostly the noodles.
It's hard because we want them to stay on track with us.But for kids taking antibiotics and with weak stomachs, it's important not to make eating a battle. You can just serve food she likes alongside what you are eating-- just make one option she would really enjoy and you are *sure* she'll eat. In time, she'll be back to her old self and you can 'wean' her off being only temporarily catered to. UTIs also are painful, too, so that may be having some effect as well.
And don't have junk food accessible. You are able to put things up out of reach. Do it.:) That will eliminate a whole other battle.