Question about Screen Sharing

I will be moving away for school to a different province and I would like to be able to take control of my girlfriends MBP over wifi, she is not the best with troubleshooting computers.

I have a 15" rMBP and she has an 13" MBP that's a few years old. We are both running 10.9.3 and I'm looking into some options as to how I can control her computer over wifi if she has a problem. We will be both on 2 separate networks.

Any suggestions?