R.S.
Regardless of her condition start talking with her about becoming a woman. It is a natural thing though be it early. My daughter knew at an early age what pads and tampons were and about having a period once a month. She thinks nothing of it.
This is a crutial time for you to instill in her confidence about herself. Although she is maturing so quickly and she may have a condition, there is nothing wrong with her. This sends a message to her she is "not good enough" - instead she may have a medical issue. - it is all in the wording and the way you handle it. Try not to freak out about it in front of her. she is scared too and looks to you for re-assurance. My daughter is much older almost 10 and I worry she is developing so quickly too, but either way it is something we deal with and pray about. We have to re-assure them each step of the way---even if we are re-assuring ourselves as well.
Sounds like you know not to give her too much information - be brief and factual. I started by having my daughter get the pads for me when I was on my period. When she asked what it was for I said oh when your a women you have a period once a month. - very matter of fact and non-emotional -
Hope this helps. You have every right to be considered and I hope you can find help for her.
Best wishes