Hmm... I have the same problem with my bro. I just hit him a couple of times everytime he uses it. He tends to forget so he always gets hit.
another option: get a super secret growth serum and mix it into her breakfast ... once she is at least two heads taller than you your clothes wont fit her any longer
find out her hated color and choose your clothes based on it. Offer her a lot of snacks... the fattening ones.
Buy her ice cream every day and in two month you would get her upgraded version(5 kg increase at the very least).
I'll be honest. I thought of something inappropriate at first when I read this, but then I started to feel annoyed. I can relate when your sibling ruins your stuff. That said, I mistook you as a "brother" until realization kicks in, "Wait... what sister would wear their brother's favorite clothes?". So yeah, hide your clothes in somewhere not even your sister can find it. Good luck in your endeavor, Madam President.
I never understood the not sharing clothes. Grew up pretty poor. Shared clothes all the time when we could. I guess sit her down and have a real talk about how it bothers you a lot. Invasion of privacy and what not, instead of the arguing. Make the mood serious and non hostile and then try.
Here's a bad idea: If you have different chest sizes, if you smaller than her, buy tight fitting clothes, if you bigger than her, buy those that sag if not fillled, or shows emphasize on the chest area. If you two are about equal, buy clothes that you don't mind wearing, but will make her uncomfortable in, providing that you like it though. Like showing the belly, or long sleeves... etc.
Roam around nude and make her roam around nude too till she washes the clothes. Use violence and seduction as required.