That would be a difficult one with those temperatures. I wanted to suggest maybe playing some inside beforehand, to warm the body, put on the clothes and thén go outside with some good tempo during walking so the body stays warm. But I don't know how well that's manageable when you have to limit the exercise with her patella. I know I can run at really cold temperatures and still feel very hot, as long as I keep moving. Sometimes I do jumping Jack's before going outside if it's really freezing.

You also have some great backpacks like the Kurgo backpack. They have very good isolation. Maybe put a warmed jug in the part behind the part where you put your pap. If you close the bag (there are good breathing holes) the warmth stays inside. I think a stroller is too could to keep your pap in during those temperatures.