Thanks for the query.
she might be suffering from a fungal infection
It is called as tinea cruris
Treatment with oral and topical anti fungals will give you a good result.
Try to keep the area dry, for better and faster relief.
Please meet a dermatologist
and discuss regarding this.
Let me know if you have any other doubt.
you can ask a direct question to me on this forum, following the below link.
Wishing you a good health.