Why does what she did bother me?

My mother sold my drumkit over the weekend, I don't know how much she sold it for but she gave me £50.

Thing is I didn't use the kit very much and I wanted rid of it for a smaller and better one since that kit was old and not very good.

Yet for some reason the fact she sold it annoys me. Maybe it's because I'm reminded that I'm not completely free of her. I thought I was since we never saw or heard from each other but I guess that was wishful thinking.