Should I tell my mom that I don't want my Christmas gift from her?

She kindly gave me a dressing gown but I hate it... mainly as I have two already - both from 5 star hotels which I really like. I kept the second one in perfect condition as a spare and wear my light cotten one from a hotel in Bangkok. Now I was given some big wooly one which I don't need/want and it is too short as it doesnt cover my knees leaving them cold. What should I do? I live with my mother right now but will be moving out in February. Should I just wear the gown or tell her the truth? I wore the gown for an hour but have taken it off as should i soil the gown, i wont be able to return it... should i just be honest with her?