J.H.
That's most likely a yeast infection. The best treatment is a topical application of miconazole, the same cream you buy that comes with the applicators (the 3-day is more than sufficient). Apply with a tissue after cleaning her 2-3 times per day until symptoms disappear, and follow with an extra 2-3 days. My girls have always been real sensitive to them, so I had to stop giving them baths (they both take only showers) and I always keep a tube of cream on hand. Hope this helps :}