Mother mad at me

Okay, so I have always had a weird relationship with weights and diets since my mother told me when I was 15 that I needed to start watching what I ate. I was about 106 at the time, maybe 5'4". I have come a long way from there about deciding for myself what is good for me, right for my body, etc. A lot of her advice is helpful, and in the long run, I know she means the best for me. However, when does she cross the line?
This past semester, I have decided to take a semester at home because my school up north didn't offer a subject I wanted to learn more about. Since entering college I gained about 25 pounds. Ten of those pounds put me at a healthy weight for my body, about 123 pounds. However, the other 15 I agree could go. It's something I see and know I want every time I look at myself at the mirror. However, ever since I have come home, my mother watches everything I eat. I am not losing my weight fast enough for her and I do take a lot of liberties that come from running extra hard on a given day, etc. While I appreciate my family supporting me and pointing out some of my excessive snacking, is it right for my mother to get upset when I take a piece of chocolate from a pile of candy that she is trying to give away (to get ride of the temptation for herself and for me)? I have been having a low day and wanted to give into my low resistance (a different matter altogether) and I understand that this kind of behavior-eating candy when I am depressed or in a bad mood- is precisely what I need to fight against, but was her reaction appropriate? She was disappointed in me, she says. Something about that makes me upset, because it gets rid of the notion that I am doing this weight loss for me. Can someone out there who understands this help me figure this out?