OK, there are a number of options here - as long as you are happy to leave your PC on while you are away.
- You can set RadarBox to Record before you leave the house. A couple of problems here, as the Record function only records Live traffic and not Network traffic, so you might miss the aircraft. Also, with one version of the RadarBox software, the Record function didn't work - can't remember, but it might be V1.5 - this has definitely been sorted with the latest version of the yet to be released V1.6 The good part with the record replay is that you have full functionality of the RB interface, so you can zoom, pan and click on aircraft etc.
- You can use a time-lapse screen capture program to capture your screen at certain time intervals. I use iQuick Quick Screenshot Maker for this to either capture just the map or the whole screen. The disadvantage with this is that you will just have a series of pictures to look at and you won't be able to interact with the RB interface.
- You could always take RB with you to Heathrow if you have a laptop and sit in a supermarket or hotel car park and watch the flight depart and follow it as far as you can.
- If you are really keen, you could book into one of the Heathrow hotels at a daytime spotters rate - I've seem mention of this but don't know the details. The hotels usually have WiFi so you could view network traffic too! Of course, this will probably be impractical if you are on any type of timescale :-)
Whatever you do, do remember the "mission" is to get your girlfriend to the airport on time - she might not share your enthusiasm about the importance of tracking her flight!