This is great! What youre looking for is a little GPS unit with a color screen that shows a map of the terrain on which youre skiing, and indicates with a little digital pony-tailed figure where your girlfriend is located, and with a manly figure your present location, and that also gives you the speed, rate of descent, and direction of travel of your girlfriend, while sending the same information to her. And maybe you can even talk to each other!
And, of course, you can have such a thing. Simply enlist in the 10th Mountain Division, part of the U.S. Army. Because of that elite units specialized training and the advance state of electronics gear used by the military, you surely will have a chance to ski with equipment of this sort. Along with, of course, a 60-pound pack, Kevlar helmet, and an M-16 rifle. But life is full of tradeoffs.
As for walking into your local electronics store and buying it, alas, no. The technology clearly exists, but its simply not practical at the level of ordinary people. You can have a GPS that knows exactly where you are and displays that location on a screen, and she can have the same. Now, how do you get that information into BOTH units? Thats the hurdle. Communication couldnt be based on line-of-sight radio transmission, for reasons you already have delineated. So one GPS unit would have to beam its position to a GPS satellite through some sort of continuous transponder unit, such as what airliners use to beam their location to air-traffic controllers, then transmit that signal to a specific second unit, not the entire freakin world. Not easy.
Im afraid, for now, youre stuck with yodeling.
Youve got your winter gear, now get outside and use it. Away.coms ski and snowboard guide makes it easy to find nearby slopes just begging for fresh tracks.