My baby my stuff

Ok so my mother is so excited that she is a grandma first time and so she buys me a use carrier is a nice kaki peach looking color but the problem is theirs grey stains that won't come off i don't care so i buy this seat cover to it and place it on top i like how it looks and can't wait to put my princess in it first time mom. When i went to buy the seat cover i went with my mother in law and sister in law. That day my mother in law show me a car seat saying is cheap $50 i told her it's pretty but i already have the car seat my mom brought me and I'm going to buy the seat cover. She said ok and so i show her how it looks and she likes it. But then i found out that my sister in law is calling me a cheap ass that i have money and don't want to buy a new car seat instead I'm using the one my mom got probably from a store that sells used things. The question is am i wrong for using something my mother bought me for my baby? Even if it's used? Knowing i can afford to buy a car seat but choose not to because i love anything my mother gives me and won't disrespect her on not using something she got for her first grandbaby? Should i even explain myself to my sister in law or just beat her ass for thinking calling me a cheap ass haha just playing but for reals thoe is there something wrong with the way the carrier looks???