If I gave one of my girls something of value and she threw it away, I'd get it out of the trash and claim it as mine now. It became up for grabs the instant it was discarded.
If that car is at WalMart, I'd have it towed to storage in a NY second so it's safe --and inaccessible to others-- and then I'd fly out there and retrieve it or hire someone to drive it back. All the paperwork is in your name, so it's ready to go on the market.
If Sweetheart thinks she's old enough to go off on her own, it's time to let her go. This young generation's sense of entitlement is mind boggling. Who ditches a free car?!
Can you see why I retired early from teaching high schoolers? It sure wasn't the literature that degenerated in the last ten years.