What a fabulous friend you are - I truly don't think I could bear to be so cold for any prolonged length of time!
Wrt to warmth, equip yourself with thermal leggings and tops and wear them day and night. Would your friend be offended if you were to take an electric blanket to her house and leave it there for your visits?
Thinking of food, do you both go out shopping for food when you're visiting? I was thinking that if you had cash, you could quickly jump in and pay the bill while she was packing.
I believe Amazon sells food now, is that an option for delivery?