Hi and thanks for this query. I a so sorry to hear about this blood build up and the endometrioses. Hope together we get answers and solutions to this. Blood building in the uterus points to the fact that there is a problem with the passage from the uterus through the cervix and vaginal to the exterior. She needs a careful exam for the patency of this passage. .In Virgins, impeforate hymen could be a cause. Also, vaginal synechia or cervical infection with scarring can block this passage. At times, simple dilation under anesthesia can provide a life long relief unless otherwise. It takes a careful interview, physical exam and a few test to address this, Please, meet with your OBGYN and press hard suggesting the above possibilities. Sure you will come out with some positive results. I wish you well and hope your daughter soon gets the relief she deserves. If you have more questions, please follow up and i shall provide more answers. Thanks for using our services. Dt. Ditahm, MD.