If you or she can afford to get I highly recommend halogen heaters they heat up a room a treat and are very cheap to run, I first got one each for living room and mine and dds bedrooms when we lived somewhere with shockingly bad and extortionately expensive.
Other than that all the usual that have mostly already been mentioned - wear layers and warm clothes, hot food and drink (flasks a good idea or at least teapot with a cosy)
I feel the cold and in winter I've been known to wear the following to bed:
Leggings, vest sometimes also t-shirt, bed socks, AND pyjamas. I've been on occasion worn a woolly hat!
Extra blankets/throws for in the living room or bed
Electric blankets are good and pretty cheap to run.
Head to bed early even if not planning to go to sleep, I used to head to bed as soon as dd was asleep at like 7/8pm and read or listen to music or watch dvds (pre streaming days and no tv aerial connection upstairs/in bedroom) until I was ready to go to sleep.
I spent a lot of time in libraries/community centres in order to not have heating/lighting on when dd wasn't home that was when I was really on the bones of my arse!
I could always find something to occupy myself in the library.
Community centres could be a little trickier.
Is she eligible for warm home discount or winter fuel payment and if so has she applied?
The most obvious one is very tricky to risk at the moment though which is ensuring she's with the cheapest supplier cos the energy business IS such a flipping mess at the moment with firms going bust etc