I want to be able to put her laptop/cellphone onto a vehicle.
You need very long arms for that
Does anybody know a good vehicle to use for this?
I don't think the vehicle is critical. Almost anything will do, like a modded toy R/C car - It will be frog perspective though, but that may be the fun part of it
My wife has a samsung S3, can I use it? Or can I use the laptop?
The S3 is probably best - low weight and an awesome camera (at least the back side cam), way better than most webcams. Make a vibration dampened hulder for the phone, perhaps with a charger onboard.
Mod the car to be steered via touch tones (DTMF) and you should be good to go.
It might be a good idea to make it control the pan/tilt via the interface as well.