During the week before her withdrawal bleed (she's on ortho tricyclen low)the bottom of her inner labia closest to the perineum, get severely irritated to the point where she can't stand to wear underwear, or have anything touching them. When nothing is touching them, they sting. Her inner labia are longer than her outer labia, so they come into direct contact with her clothes. She generally wears pretty standard cotton panties and she's tried a few different detergents, including some without fragrance, and it doesn't seem to make a difference.
Does anyone have any ideas of what this could be?