Check Cabelas.

They have a heated vest.

Something like electric socks, only for the upper body.

If I remember right, its only like $80. Definitely less than a new jacket, and I think it would keep her nice an toasty in the stand.

If I also remember right, one battery lasts up to like 8 hours per charge, so she could alternate it on and off all day when she gets chilled and be comfortable for an all day sit.