since the old hard drive is out, you can get an external enclosure (caddy ?) to hook up to new macbook, by migration assistant (Application > utilities > disk utility > migration assistant) to transfer your data over to new macbook. Sure you can put the old hard drive back in to the old macbook and give to your girlfriends parents. Meanwhile it is a worthy investment to get a hard drive as external drive to back up your macbook
using the newly bought enclosure.