My kid knows nothing is personal. She'll be 16 this year, at any time of any given day - anything can be searched. Her mom and step dad or myself... Have purchased everything she loves.
In turn, she doesn't give us a reason to need to look through anything personal. She's not in with troublesome students, gets descents grades, and works when she can for her own money.
In return - I've been putting cash away in an account, so she'll have a nice $10K graduation present. We treat each other with respect.
It sounds to me like you have strong feelings about what you believe - which are in direct opposition of what your mom believes. I'd imagine your mom had a much stricter growing up scenario than you have - or didn't have a great family situation herself growing up. Which has turned into a fervent struggle to hold everything together - trying to be a glue to the family. Then your ideals come to light and all of that starts breaking down.
She then feels like a failure, rejected, and like she has no common ground. So - she lashes out.