Congratulations and welcome to the forum! The stress of being in the shelter may be a factor in her loss of appetite. Every dog is different and what they eat ravenously, just pick at, or ignore will vary. My four will eat Fromm and Honest Kitchen without fail, but I do give things like chicken feet, beef, and such on occasion, generally if I'm making dinner and it's something they like then they'll get some too. You may find she likes plain kibble or does better with a raw diet, it'll take time to see what works best. I recall a thread on making "Satin balls" for weight gain, you might try the forum search bar and looks for threads on it to see if it's something you want to try.