sharing is caring?!

I think you have every right to be upset with your sister. It sounds like she isn't respecting your property. I have 3 sisters and this happened in my house all the time growing up. Just tell her that you would like her to ask before she borrows your things and let her know that you don't like her wearing your new clothes before you do. If it still doesn't work then put a lock on your closet... that's what my sisters do. And if all else fails gain or lose some weight so the clothes fit you and not her. I am bustier than my sisters so they never borrowed my clothes since the chests of my tops always looked stretched out and funny on them. Hope ou can work things out for you!