This is hard, and will depend a lot on your situation, anon. Do you still live with your mother? There might be no way for you to escape spending time with your mother without further abusive consequences. If there’s no way that you can escape spending time with your mother, I recommend making time for yourself after that contact to practice healing behaviors and reaffirming your worth as a person, reminding yourself that what you experience is abuse.
If you don’t live with your mother, I recommend making yourself very busy on mother’s day. Make sure your mother knows ahead of time you’re ‘going out of town’ or ‘have serious errands that can’t wait’. If you must, make a ‘happy mother’s day’ call when you know your mom won’t pick up, or send her a text, then turn your phone off for the rest of the day.