Of course I have to be the exception. Alway am. Puppy chow is the only thing that keeps weight on my 10 year old boy. California Natural Lamb and Rice. 591 calories per cup. BUT.......he does not get it every day. He gets it maybe three times a week. That said, since he has gained back the weight he lost in a weight loss episode similar to what you are seeing, I am switching him off the puppy chow and on to Innova at 557 cal per cup. I am making the change for the reasons Diane noted (and other reasons as well)
As far as Da Bones weight loss itself. We never did really figure out what caused it. Best guess is he had stomach upset (or maybe even an ulcer or the beginning of one) from Glucosamine. I had started him on it only because he was aging. No real issues. As soon as I stopped it, he started to get better almost immediately. Maybe that was it, maybe it wasn't, but he does not get Glucosamine now and he is doing great.
Probably not much help but I wanted to wish you luck with your girl. My best advice would be to look at everything she does, everything she eats, any recent changes and go from there. You'll figure it out. Good luck!
Oh yes, my youngest hound recently had an ultrasound of her kidneys. Not invasie at all and cost $63.00. I would do it to rule everything out I could. Again, good luck.