We took away my 85-year-old mother's car keys and she is no longer speaking to me. What should I do?

You did the right thing. Of course she's mad! She's lost her independence. You had the courage to intervene and that is hard.

Please try to make sure she has transportation to where she wants to go, either from family, as senior van or other means. Eventually, she will get over it if she knows she can't bully you. But she needs to know she can go places.
Carol