Is it wrong for your mom to yell at you for buying something with your own money?

I bought a skin for my laptop from skinit with my own money. When it arrived, I was satisfied with it. My mom got really pissed off because she thought it was like a plastic cover, not a skin. I explained to her that's what the "skin" in "skinit" meant. She yelled at me again for buying something completely useless that won't even protect your laptop and forced me to return it. And I'm like, "I used my OWN money to pay for it, not yours! It's mine and I can do whatever I want!" She disagreed to what I said and supposedly we're driving to the post office tomorrow to refund it. Is this justifiable?