used crib mattress

Last night one of my friends gave me a crib mattress that her son used when he was younger. My husband and I have a brand new nursery set and had planned on purchasing a mattress for the crib however she insisted I take her old one to save money. My question is are there any risks with using the mattress? Should I just get a new one? I didnt want to hurt her feelings but I have been very picky with my child lol 🙈 Ima FTM by the way!