Hmm....maybe a small space heater - some are very quiet(though what is quiet enough for a cat???LOL) - with thermostat control that could warm the immediate area where she sleeps...you could put a timer on it as well.

The only other thing I can think of is thermal underwear or trousers! Leg warmers...hey, cats can always use a new toy!

Wish I had some good ideas for you!

Catty1