FYI: Someone, perhaps threnkeldwingnu, was up in the Sierras in the Yosemite area and he said it actually snowed up there (a very little bit...I think it was the weekend it rained here) causing him to cut his stay short. I don't expect it is going to snow much soon, however, you might consider having ZsuZsa take the heavier sleeping bag. If it is too warm, she can always unzip it. But my experience is that if you don't have a bag that is warm enough, well that's a miserable experience. Also, you might want to find a Therm-a-rest or other camp mat for her to borrow. It will both be more comfortable than sleeping directly on the ground and also insulate her from the cold ground.

Anyway, a couple of thoughts I hope are useful.