If she's just using this in an emergency, and you'd like to avoid spending a lot of money on a tent, you might consider an 8x10 coated nylon (not hideously expensive silnylon) tarp, plus an REI bivy sack:
http://www.rei.com/product/794292/rei-minimalist-bivy-sack-regularhttp://www.rei.com/product/766383/outdoor-products-coated-tarp-95-x-8 (these come in 3 different sizes - enter "tarp" in the search box)
For about $140, you've solved the whole shelter problem. The bivy offers several advantages: it's weatherproof, which means it will add some warmth (OK, slow heat loss) to whatever you put in it, and protect against blowing rain or snow. If you use a fleece bag, it provides a shell material for it. You don't need a separate groundcloth (I never used one with it.) As I recall, mine was fairly generously cut, and it only weighs a pound and change.
The tarp isn't light compared to silnylon, but it is fully functional. There's also a 10x10 size, for $10 more, that is even moreso - using a hiking pole, it pitches nicely into a wedge that can be pointed into the wind. Not a palace, but it would work in a pinch.