The other thing you might want to consider if the ABs don't have the desired effect is whether she has enough fat (especially animal fat / protein), and iron in her diet. DS has been prone to what we term butt vomit, and would poo up to six times a day at three years of age, we thought it was acidic food that was the problem and cut tomatoes and most fruit, but have noticed a huge improvement (to the point that we have re-introduced everything else back into his diet with no ill effect) since making his diet high in red meat. We previously ate red meat rarely. We had thought that it may be lactose intolerance but it seems that he needs a high fat/iron diet. His dad is the same - he has IBS and was at his worst when vegan, he had to re-introduce red meat for his health. Lactose intolerance should show up in samples too. Oh, and after an extended course of ABs it's not uncommon to have a period of lactose intolerance as the ABs bugger around with the bacterial balance in the gut, probiotics can also help with this. According to my doctor, it can take around six weeks for this to subside following an extended course of ABs.

Hope it clears up soon!