Boundaries are for you. Your Aunt doesn't have to like or approve of your boundaries, but if she crosses them then she will learn there are consequences. I learned that when I set a boundary, it is perfectly fine for the A to have their reaction to it. Their reaction does not have to change my course.
If you're not ready to meet for coffee, then that's okay too. You don't have to get pulled into anything you're not ready for or aren't interested in.