my sister was borrowing my clothes

last week i noticed this weird stain on one of my old t-shirts, and when i asked my sister about it she said shes been borrowing some of my stuff lately cause her laundry has been piling up. at first i thought maybe its just an oversight but now im not sure if shes really just taking without asking, even for a few days at a time which feels like a long stretch to me. anyway we had this big argument about it and everyone said she needed more responsibility, but i cant help thinking am i overreacting or is there something else going on? still wondering about this.