How to tell a cousin to never borrow my clothes?Anyone with the same situation?

My cousin is also my neighbor and she likes to raid my closet to find clothes she would like to wear. I don't know how she developed this habit, but since she's a close family member, I just ignored it. Worse, she would return them to me, unwashed so I would have to add them to my laundry. Once, she took a blouse I should wear to office. I was irritated since I was already in a rush to prepare/look for another one. I told her to let me know when to borrow my clothes with a frown in my face. She was hurt and left my house in a rush. She never talked to me for days. I don't want her to borrow my clothes again but she's asking my permission again. What should I say not to her that much? She might tell my other relatives that we had a misunderstanding just because of a blouse.