I know it sounds strange, but my son used to get them from the baby wipes I was using! Every time I got near the bottom of the container where the blue "you're running low" indicator line was -- pow --there was the rash again! (only took 2 containers to figure it out!)
When you buy the yogurt, make sure it has active Acidophilus cultures in it.
I was prone to yeast infections, too. Now I watch my acidic intake, including vinegar, pickles, yeasty breads and rolls, AND sugar intake ... etc.
Also, if she's potty trained, stick with 100% cotton panties...no nylon or polyester blends!! **This is all part of the "air" situation. Make sure she's wiping from front to back, too.
That's all I can think of right now, aside from calling her doctor back and getting better advice...or finding a different pediatrician.