What cream is she using. It may be that she simply needs a different one or a stronger one. I just recommend clotrimozole that you buy over the counter at the drug store. It will say for ringworm and athletes foot and jock itch but a yeast infection in the diaper area will clear up with it really well.

The doctor's version for my daughter years ago was half clotrimozole and half 1% hydrocortizone cream.