reptile heating lamps are easy to get ahold of, and easily portable. When you notice she's frequenting a new spot you can clip it on there, or around it, and she may enjoy that.

now that it's getting to be winter time one of our kittens (tiny little runt) has started sleeping in the turtle's tank under his light at night. They put off good heat and are quite portable.

they also sell ceramic ones that don't put off light, so that the light won't bother her.