sr5599, that is soooo cool that your GI is in favor of probiotics!
itainteasy, since you questioned it, I've recently read some scathing articles in the alternative community on Prevacid and sister drugs, partly for reasons you mentioned. They recommend upping the use of digestive enzymes and even a teaspoon of organic apple cider vinegar (diluted in water) a day to combat excess stomach acid. Apple cider vinegar also fights candida. Neither of these things can hurt your daughter and just might help!
Unfortunately, all those Ensure-type drinks are super loaded with sugar... If you can get her to substitute plain yogurt smoothies sweetened with honey (and I add a bit of Stevia and natural vanilla--no sugar added) it would be a great solution. Jordan Rubin in his book, "The Maker's Diet" gives a recipe for smoothies that includes putting Virgin Coconut Oil (as spookyhurst recommended) right in the blender when you make your smoothie! This not only fights candida and adds beneficial omega fats, but will also add calories, which I assume is part of your goal!
In the very beginning when my son embarked on this diet and new way of eating, I had to do a lot of convincing that there are thousands and thousands of people world-wide who follow this diet. Although he wasn't interested in actually reading the books, I showed him Rubin's book, Elaine Gottshcall's book ("Breaking the Vicious Cycle"), the large number of cook books written which are compliant with this diet, and the online forums where it is discussed. He seemed to need to know that this wasn't just some hair-brained scheme of his mom's.
Imagine....!
Because my son was 15 when diagnosed, we went to our children's hospital. Just thought I'd share that our doctors were not helpful or encouraging about
anything we did (diet, probiotics, etc.). We endured a lot of "poo-pooing" when asking about
such things. Maybe pediatric GIs are even more conservative and "by the book" than other GIs, I dunno. I liked them all very much, but I do wish they were more forthcoming about
our options.
One last thought, and sorry for rambling... If your daughter's GI did prescribe Flagyl for a C.diff infection (I would REALLY get to the bottom of this. I realize she's off Flagyl now, but C.diff can be extremely hard to eradicate and often comes back), you may want to consider adding one of the probiotics sr559 mentioned--Florastor. There are scientific studies now which prove its effectiveness against C.diff (you can google it and read up on their website). Many doctors prescribe it for their C.diff patients and tell them to take it indefinitely. It has a different strain of probiotic not found in the others--this is what makes it uniquely effective against C.diff.