What Causes Blistering Rash Between Natal Cleft And Vagina?

my 13 yr old daughter is suffering with a blistering rash which starts at the begining of her butt crack to the begining of her vaginal area the dr.s are stumped. thet think it looks like the shingles and are treating her w valtrex . the problem is that they dont feel like shingles can develope in that area. they cultured the area on Mon. 5-16 but wont have the results back for 7 days. Any idea what it could be ? im desperate to find out. its so sad she is in so much pain