So my mother knows about my self-harm?

[Saoirse]

(Long! Sorry!)
So my mother found a pack of razor blades-- shitty ones that I haven't used for a while, so I'm not sure where she found them. The point is that now she knows I've been cutting again. It's been happening for a while, really. Anyway, I've got some other s**t going on- eating disorder, suicidal ideation, that sort of thing.
The thing is that I really don't want to tell her any of that, or anything about my self injury, because she's already freaked out.
I mean, I don't blame her. But she's not letting me use any social media or whatever, checks my internet history and only lets me use the computer in front of her, doesn't let me use my phone, tries to take away anything sharp.
She's been saying we'll have "a discussion" for almost a week now, but that's not happening.
The thing is that talking to my friends is one of the few things that keeps me reasonably sane, and being isolated isn't going to help. I can't leave the house except for school, and I'm going mad.
I can't stand not having control over my own life, and it's WAY more triggering than any of the things she's taking away.
I've been wondering if I might be depressed, but I've raised the issue in the past and she basically told me that I wasn't.
I feel completely trapped. I have no idea what to do. How can I explain to her that none of these things are helping without worrying her more?
I just don't know how much she knows or what she thinks, and it's understandably a bit of a touchy subject.
What can I do?