I definitely understand the paranoia you have. Although not entirely the same, I hate being touched at all, and have slowly (sometimes it seems excruciatingly slow) been getting used to my friends and allowing them to give me hugs and such. Even then, they all know to ask first, and only occasionally forget.

I get the same feeling you describe when I have a cringe reaction or even a reflex to fight. They immediately apologize, and I do my best to remind them that it isn't their fault.

What came to mind for me, when reading this, was maybe you could do something for your mom, like cook a meal or make her something. You mentioned agoraphobia, so flowers may be hard to get... I just wonder if some small gesture, as an apology, would say what you want to say, without actually having to bring up the topic itself, since she knows it's an issue for you.