Could your mother have fibroids? Extended heavy bleeding is a symptom. I had a massive fibroid during my pregnancy which caused bleeding on and off. I was told that if it didn't go away that they would have to cauterize it.
Other thoughts, I also had hormone problems, have your mother find out what is wacky with her hormones through blood tests. I have PCOS and metformin fixed my six week long heavy bleeding.
Maybe something helps, dunno.
Wife, and mother to a small fairy, a demolition expert, a special new someone this fall and a small dachshund.