Why is my daughter so angry? How do I explain it to her?

I met a girl at a dance club, and let her stay in my daughter's room for a week, my daughter is at college, this weekend she came home and found bra, panties and a thong that she never bought. She said the bra was same cup but wrong size etc.. I never thought this would happen.,

Why is my daughter so angry? How do I explain it to her?
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