I'm so sorry to hear of this development in your mother's journey. Your family is in my prayers.
I did a search on "cancer hormone therapy" and found this link:
I don't know if it's any help. Seems to me that if your mother is post-menopausal, that hormone therapy to dampen hormones would have a minimal effect. But I have no personal experience with your particular situation.
Is your mother in frail health otherwise (aside from dimentia)?
You have been such a wonderful advocate for her care all this time. Say a prayer, then trust yourself to make a good decision.
We're here for you.