Sheet of clear plastic, could be a shower curtain liner even. This can be useful if a window gets broken (smash and grab, or the window fails to roll up, etc). Something clear you can tape over the window to keep rain/snow out.
That's a great idea! Never thought of it before but that could really save the day. That and some T-Rex Tape would fix about anything.
I also second the recommendation for a warm sleeping bag. Chains are great. A shovel, traction mats and a four-way wrench are great items even if she's not that mechanically inclined. Always have some tools to self extract even if doing so might require some help from a good Samaritan.