Monty used to sleep in our bed all the time despite having his own bed in the room and we thought he'd never use his own bed.

Daft as it sounds, we put his bed infront of the radiator and now every night when he hears the heating click in, he slinks off our bed and into his own as he knows it will be warmer than ours!!

I agree with the part that staffies feel the cold more, but they are snuggle monsters so its not surprising give both traits that they sneek up on the bed,

you could try raising her bed off the floor, stick it on top of something not to high, poss 6 inches off the floor. keep her bed next to yours,