I am assuming she has been checked for all the usual suspects, yeast, infection, std's, previous sexual abuse, pelvic floor integrity, etc.etc.? She'll need to get her yoni in really good shape before her next labor. It sounds, to me, that her yoni tissue is not in optimum health and or she is not lubricating well before penetration, which could be hormonal or emotional response. Or, sex that is too rough. How was her birth? Physical and or emotional trauma experienced during birth can create a friable yoni. Is she pregnant now? Have her hormones been checked? Good food, kegels, kegels, kegels, hydrate, perineal massage, use time and and warm oil (almond, olive coconut) for sexual lubrication. How long ago was her first babe?