Even though your mother snooped through your things is there anyone you can trust more than her with your keys?
In my experience parents who care snoop, it's just what they do.
Both my parents, who only spent 6 weeks together in their entire lives, were snoopers.
My father was still snooping when he had senile dementia. Mother snooped when she took me in to keep me out of a rest home. I was in my late forties at the time. It bothered me a little until I realized that she had been doing it my whole life but only because she really cared.
My step brothers and I were beaten once as a child, I came up swinging my brothers joined in and we sent my mothers boyfriend to the hospital. We never saw him again. He had a lot to think about for the two years he spent in prison for his crime.
One thing to remember no matter what your mother is always going to be the only mother you are ever going to have. If you back away do it gently, at some point in life you might actually want her in your corner.
If it had been the step father who was in your flat my answer would have been different.