Tanya, my dad is exactly the same!
He always wants to help and be involved; like, if i've had a fight with my friend, he insists that I tell him. And even if I say, "no, I don't want to talk about it", he gets mad, and starts saying that avoiding it is not the answer, blah blah blah. He doesn't understand that I don't always want to talk to him about certain thing.
Then he tries to guilt me, saying, "oh, i'm sorry, i'll never talk to you about things again, your life can be free of me irritating you, do whatever you want, and don't try to do the right thing or get help from people who know."
it's hard for parents to understand sometimes. I bet your mom wants so badly to be a good mother to you, and to be involved with you very difficult situation right now that she's a bit too close for comfort. Just try to explain how you feel calmly, and if she still doesn't get it, well, this is still your baby, and you have the right to tell her to back off.
And no, you're not being unreasonable.