My dad knew he hadn't much time so it probably helped. If your mother has a unique story (war, achievement, migration...) maybe she'll be inclined to tell it. Also, it's easier to talk about others, so you could ask her about her parents. Then you could switch to her.
I'll emphasize that like anyone born before smartphones, she may wish she had more pictures and videos from decades ago. Assuming that, she may understand your point of view and accept being the subject.
My dad knew he hadn't much time so it probably helped. If your mother has a unique story (war, achievement, migration...) maybe she'll be inclined to tell it. Also, it's easier to talk about others, so you could ask her about her parents. Then you could switch to her.
I hope it helps.