Postmenopausal bleeding is always a reason for getting it checked out. It would be important to know what was your doctors conclusion after she measured your endometrial thickness - the normal thickness of the endometrium is below 4mm, and 11mm is definietly an indication for an endometrial biopsy (taking a sample and investigating it).
It is important to know if you are taking any medicaments for menopausal symptoms, maybe? In that case, a thicker endometrium could be caused by those.
Reasons for postmenopauseal bleeding can be totally benign, but unfortunately sometimes also malignant and in that case the sooner the diagnosis is being made, the better are the chances.
I would hardly suggest you to visit a doctor and interrogate him about the background of this hyperplasia and about doing a biopsy, to rule out a malignant process.
With best wishes, a going-to-be-doctor in a few months