Hello, and welcome to HCM!
More details on your mother's medical history (what kind of major surgery, why was a kidney
removed, has she ever had cancer before) would be necessary to truly answer your question. In general, heavy vaginal bleeding
in a woman your mother's age is concerning for a few problems. With the uterus
appearing "thick" on imaging, endometrial cancer
and fibroids are certainly possibilities. Both of these problems can cause heavy bleeding. She should be evaluated as soon as possible by her doctor, who may decide to do further imaging or blood tests.
I wish you good health, and thank you for posting on HCM!