Please help - dog with no appetite

Hi,
I have a 17 year old dog, she has never had any interest in food - but recently the problem has become much worse. Her weight has dropped from 19kg to 12kg.
Our vet has been unable to establish a firm diagnosis, but considering the dogs age, neither of us want invasive tests. Palliative care is the option of choice, and apart from the complete lack of interest in food, the dog is doing well.
Initially, I requested some anabolic steroids to boost her appetite, and she was prescribed Nandralon for two weeks - it seemed to work for a few days only.
Now, instead of trying an alternative anabolic, the vet has withdrawn the Nandralon, and prescribed anti-inflammatory steroids, ie prednisolone - though she admits there is no underlying inflammatory condition, and is propsing these as appetite boosters.
I am very unhappy with the situation, and hoped someone could advice if there are any natural/herbal appetite boosters that could be tried.
Thanks for your help, as I'm very,very worried about my little dog, and feel that time is very much of the essence.
tigerheart