Hmmmm...

You, your girlfriend, 2 sleeping bags, & a tent...

Seems to me you warm her up by zipping the 2 bags together. If done properly, neither you nor she will notice the ambient temperature in the tent (which will increase a small bit, no doubt). <img src="/images/graemlins/grin.gif" alt="" />

Cheers!

David <img src="/images/graemlins/wink.gif" alt="" />