Type of rash??

So my little girl has a rash on her vagina. At first I thought it might be diaper rash, but then it wouldn’t go away as I was putting cream on it. It has spread and it will look like it’s getting better then get really red. She doesn’t seem bothered by it, but obviously I am concerned. I am going to take her to the doctor in the AM, but am curious if anyone has had this happen to their little one? She is 16 months old. Thank you.