Is she right to be mad at me?

A long time ago when I was like 12 (I’m 21 now) my mom gave me a green dress that was too small on her. She had a matching dress to it and I didn’t think she ever wanted it back (honestly I forgot about it because it was like 9 years ago). Well last year I cleaned out my closet and I was throwing a bunch of stuff out and not really paying attention. Today my mom asked me to bring her down the green dress (I still live at home). I explained to her that I think i got rid of it when I was donating my old clothes. She is extremely upset with me and she said she told me not to get rid of it because she would want it back if I didn’t want it, but I don’t remember her saying this. Is she right to be mad?