Thanks for the replies.

My parents actually went out to the bike shop when they were doing errands and picked up a replacement quick release. When I put it on the bike and tightened it, a piece of plastic snapped and shot off of the thing. No idea what it was or what it was supposed to do.

The QR seems to be holding the seat fine for now, but it seems like a really cheaply made, flimsy part. I'm definitely contemplating replacing it with a nut.

Also going to check out the hardware store to see if I can repair the old one.