Your kid likely has Candida. I took Nilstat for 10 years, to cure/suppress my ulcerative colitis. Life was fairly normal during that time, but my health slowly degraded over time. Until I had major liver problems and was forced to stop the Nilstat.
If I were you, I'd get her off Nilstat and have her take a probiotic called Threelac. As a short term solution. The only long term solution that works is diet/lifestyle changes.
If you want to learn more about what I did, I posted a nice summary below.
Concerning probiotics, except for Threelac, I didn't really feel they helped me at all. If my Candida was under control, they didn't seem to do anything. If my Candida wasn't under control, they made my bum itch sometimes. In general, probiotics are just not strong enough to make a difference, especially if you're comparing them to an antifungal like Nilstat. That was my experience anyway.