Thank you for your question
My name is ***** ***** I shall do my best to help you.
Your sister has no right whatsoever to enter your home unless you invite her in.
When she is in the property she has no right to go through the attic again unless you consent to her doing so.
Simply inform her that so far as you are concerned she took her share of the items when she attended the property with your late sister and that any remaining property is yours to do with as you wish
This is in fact the legal position
Please ask if you need further details