How to get a dog to use the stairs?

My dog is a 7 month old doxie/chi mix. She's a rescue and had a hard life before I took her in (she was found Ina dumpster). Well, I like to take my dogs to my mothers house to play with her dogs in her 1 1/2 acre yard. Well Bella (the dog in question) is smaller than the others and gets tuckered out easily so I'll bring her in for a portion of the time there. Whenever my mother and I go up stairs, she follows, but when we come back down she just stays at the top and whimpers for me to come get her. How can I teach her to go DOWN the stairs? Food isn't really working either...