I am now mid 70s. When I had this degree of post menopausal flooding in 2022, I went to A & E and they put me on a fluid drip and also a tranexamic acid drip. The bleeding slowed down after about three hours.
The cause of my bleeding was large, degenerating fibroids (I'd had a previous diagnosis of fibroids some years before and had also had a bleeding uterine polyp removed). I also had a thickened endometrium for which biopsies were taken. I had endometrial hyperplasia without atypia, which is low risk for developing abnormal cells.
I had ultrasound and internal ultrasound, a CT scan and an MRI scan because bleeding after menopause is considered potentially malignant until proven otherwise and I was fast tracked for the scans.
Unfortunately the radiographer who had done the initial ultrasound report considered that one of the fibroids, which had enlarged in size over the preceding 5 years to around 10cm rather than shrink, looked highly suspicious for a uterine leiomyosarcoma, which is a very fast growing malignancy with a poor prognosis and total hysterectomy was recommended. Because of the size of the three fibroids, my uterus was enlarged and I would have had to have had a large vertical excision to remove the uterus.
However, the radiographer who reported on the MRI considered it was a highly vascular degenerating fibroid (it can be difficult to differentiate between the two). The MDT agreed to conservative treatment and I declined total hysterectomy in preference to trying hormones to reduce the thickness of the endometrium.
I had a Mirena coil fitted to release low dose progestin but that expelled a week later. I was then put on 12 months of low dose Provera which did control the bleeding and reduced the thickness of the endometrium to the width expected in a postmenopausal woman.
Your mum needs to ask her consultant about blood test results and starting prescription strength iron supplementation. I became very anaemic with low ferritin and was put on ferrous fumarate for several months.
I hope she can get this sorted.