I think that kind of like bodily autonomy, boundaries with a kid are meant to be a little porous when they're small; as they grow up, the two of you learn to un-merge as they grow more and more autonomous.

But I wish you the best of luck with your mother. I'd volunteer to help, but I don't think a muffled stranger's voice on the phone telling her, "Your daughter isn't coming this weekend," would help matters at all.