congrats on finding little Leslie and i'm so happy for the happy ending of this story!!
i wish you and your family and your MIL and Leslie well as you spend lots of time together!!
and yes i think it would be a great idea if you guys got your MIL a doggie car seat or a crate to be put in when driving so this won't ever happen again and you'll all feel better with Leslie safe and comfy in the car!!