The Antibiotic could actually be making it worse, but, it's not a good idea to stop Antibiotics mid course, either. On to what will HELP:
First off, try adding probiotics and enzymes to her daily food (can usually find good ones at your local pet store or pet supermarket.)
After the bland turkey, try feeding her raw chicken for a few days. If possible, buy from the same free-range, Antibiotic & additive free meat counter they sell human food from at your local farmer's market/coop/health food market. Definitely check into changing her diet from regular "advertised on TV" grocery store food to mostly raw supplemented with really good 'healthy' cat food.
In the meantime, you can give her slippery elm to help. One teaspoon of powder with enough water to make a runny paste. Some cats love the taste, or you can mix it with her food, or, if you have to, ask for an "oral" syringe (not needled!) from your local pharmacy and give it to her that way. Always remember to aim the syringe at the middle of the tongue in line with the cheek pocket *across* the mouth, not directly down the throat! Oh, 2 times daily (over 15 lbs, can give 3 times daily.)
Good healthy pet foods have been discussed in earlier threads. Here's a link on why most commercial food is bad, which site also has some foods recommended by some here.
Here's another link to a recommended food (I personally haven't tried it yet): Newmans Own.
Also, check out Shirley's Wellness Cafe and search her site for "food" - Lots of good information there. Actually, just plan on reading a lot at her site - there's simply tons and tons of great information there on animal care and alternative health.
Why am I harping so much on food? Because quite simply her diet is the real key behind curing colitis. It can and has been cured many times. Good luck to you and your baby! =)