You aren't being too sensitive. That's pretty controlling/annoying behavior. Like others have suggested, I'd stop letting her read my messages or check my browsing history. If she starts ragging on your friends, cut her off: "Mom, please don't talk about my friends that way." Tell her that you will end the conversation and leave if she continues (and then do it if she does).

I would also be really annoyed with the photo posting on Facebook. Do you think she would stop if you blocked her?