My girlfriends MacBook died, and she has a time machine backup. I have a Mac Mini, and would like to restore her data to a secondary user on my computer. Is this possible? I've used time machine to restore before, but never to a secondary user. I don't know how apple id's and such would react.
OS X Mountain Lion (10.8.3)
Yes, sort of. You don't restore your entire system, via the Recovery HD. OSX probably wouldnt let you, but that would overlay everything!
What you want is Migration Assistant. It's designed for just that purpose. You can select a single user account and transfer it. See Using Migration Assistant on Mountain Lion or Lion.
If she has any apps that you don't, consider what you want to do about them carefully. See Transferring Applications for details.
How to restore from a time machine backup to a secondary user?
