I'm not a legal bod, but have been through similar with my now-ex. He let himself in and out for around 6 months until i finally got the keys back. Assuming she's a joint owner, i don't think you can legally exclude her unless you get an occupation order (not easy).
However - I think it's similar to landlords - they have a right of access, but it should be for a reasonable reason, and pre-agreed. Is she the kind of person you could discuss this with, and come to a compromise?
It took me threatening to move out and leave the house empty to get the keys back. He still has loads of stuff here, and whenever I am doing some tidying and find something I give it to him and he gets really huffy, like I'm trying to clear him out (he hasn't lived here for 8 months).
In terms of her stuff, I can't believe you're not allowed to touch it. i think technically she may have a right to store things? But you could pack it all into boxes, you can't be criticised for that. Ultimately you have to be able to move on with your life.
Another family member has moved out a number of years ago, but still pays the mortgage. Their compromise was that she would keep a key, but he would not give her the new code for the burgular alarm, so she couldn't come and go at will.
There's a good legal board under 'other stuff' where people are far more knowledgeable. Good luck.