My mom said just let your sister have the carseat. I mean I had no problem with her using it when…

My mom said just let your sister have the carseat. I mean I had no problem with her using it when she lived down here. But she's moving away 1200 miles away and she will outgrow the seat before long. And I won't have no way to get it back. And I honestly worked my ass off to get that carseat when I was pregnant so I don't want it damaged in any way. I think the other infant carseat is expired and I don't wanna put her in any harm by letting her ride in a expired seat. So idk what to do. My sis has alot of toddler rear facing seats can she transition to one of them at about 15 pounds and 25 inches long? She's very little to be 1. When I visited my sis in MN when my son was about 8 months old he rode in one of hers but he was bigger than her