You can also move her litter box right next to her bed--maybe she will smell it and will not have far to go to find it.....or you can put her in a babies diaper bad pant with babies t-
shirt over it to keep it tidy. The t shirt also will provide an additional layer of warmth. In the winter I put a heating pad under the cover of my seniors bed. She loves the extra warmth. You could try a hot water bottle under the covers, nothing electrical especially if she is going to be peeing on it, LOL!