You say she has food available, but I'm not sure from your message if she's eating it. Does she eat and not gain weight or does she just have a poor appetite? If it's the former, there may be other tests - such as thyroid - that need to be done. If it's the latter, then I would try and find things that will tempt/encourage her to eat.
Does she have other symptoms? For example, does she tire easily, seem weak or cough (possible heart problem) or is she lethargic, shaky (Addison's disease)? I'm not trying to scare you, just make sure that if she has other symptoms they are all being looked at as a whole.
Assuming it's just a poor appetite, Magtie's suggestion is a great one. We've given dogs peanut butter before too and they love it!
I have read that Alfalfa increases a dog's appetite. I know it's marketed for joint & inflammation problems, but considering the botanical name - Medicago sativa - it isn't difficult to imagine it giving a dog the "munchies" too
Maybe mixing some canned food in with dry would encourage her to eat more too.