MIL brought used crib mattress

I'm due next month and my MIL volunteered to get us a crib mattress and sheets..I hated from the get go because I know she's on a budget n all but I want a new mattress for my newborn..it looks dirty n Idk what to do Smh he's happy his mom brought it n I would be to if it was new..I don't wanna offend nobody or hurt they feelings but dang I don't wanna use it. Idk what I should do