We can't predict
I'm glad your mom is going strong! we oncologists are notoriously bad at predicting how long someone has to live.
When i talk to a family member like you, it's usually to prepare you for the worst. I say "prepare for the worst, hope for the best." it was probably hard for your mom's doctor to give you that news, and it was out of concern for you. I'm glad your mom is still with you!