Do you think its bad to sell the gift my mom had given to me?

My mom gave me a new pair of shoes and it doesn't fit my feet. No one in my family need it. I tried to give it to my niece but my sis said it won't fit them. I need money so I thought of selling it and my sister told me I shouldn't sell it because my mom would get mad and she was like "why would you sell it? Don't you have anything to do?" Like its mine now why would she got mad if it doesn't fit?
Do you think its bad to sell the gift my mom had given to me?
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