Is OTHER wrong in the post ? POST : This is going to be kinda difficult to explain, but I’ll try my best. Also, I’m on mobile. 

Some backstory; I’ve had a rough relationship with my fathers side of the family. My aunt is really demanding and more often then not gets what she wants. My cousin is a few years younger than me, and I used to be really close with her, but when she decided to do some bad decisions, I cut all ties with her. She had to move to an institution.

Now, where I live we have this very expensive national costume which we have for very special occasions, such as the national holiday or weddings and such. These would cost around 2500$. They take months to make. 
When people are around 15 yo, we have this huge celebration, and this is kinda a big deal. And most girls get these national costumes for this day. I was one of these, and i absolutely love mine. 
But since my cousin have been in and out of intuitions, I don’t think she had the time to get one. And my aunt just suddenly asked if she could borrow mine. I was kinda flustered, and didn’t know what to say, so I just awkwardly agreed. I didn’t really want to, because I had been looking forward to wearing it the whole year. 
I should note that my cousin is a bit bigger than me, and it probably wouldn’t fit, but I have a bigger sister and my aunt just assumed she would also be fine lending hers out if mine is too small.

I told my mom about this some time later, and she was all “ no, absolutely not. It’s made for you, and you only get to wear it once a year. And what if something happened to it? Who would be responsible?” So I agreed, but I don’t know what to think. I really wouldn’t like giving it away, but feel kinda bad, since she hasn’t had the opportunity to get one. And even if I don’t talk to her much, she’s still my cousin,and this day is special. Am I in the wrong?