Well, it can be done, but I hope shes worth the effort. you can buy the plugs that plug into the back of your ford deck from
http://www.installer.com/wires/ Then you'll have to get a harness for the saturn connectors (if you dont want to wire it directly) and if she still has the factory saturn stereo connectors. BUT, then you run into the problem of the factory amp. She will barely be able to hear anything without some sort of amp. How you rig this up is up to you.