I'm a little confused, and curious as to what your vet recommended that you do! Did he not give Maggie any meds or instructions for you to follow? Did he tell you the cause of this? If she has liver failure, she could die, unless there are appropriate measures taken.
Definitely do not give her ANYTHING with salt or spices. This includes the stock sorry to say. Do not give her sugar, unless this is approved by your vet. Everything that you feed her, including meds, has to be processed by her liver, so you have to feed the liver with healthy things.
"Boiled" chicken and rice, should be just fine, as well as eggs, as they have protein. You could also try boiled liver. Liver is has a ton of protein. I wouldn't really go for the tuna, unless it clearly states that it has zero, or very low sodium. There is hidden salt even in the water packed tuna.
The good news is, the liver can recover if you take the proper steps and follow treatment instructions. Here is a very good run down on what you need to know, and the things you need to do for little Maggie.
Take a look at this link, and my dog will send good puppy vibes for her to get better.
Liver Disease Signs, Symptoms, and Diagnosis
Keep us updated on Maggie, and good luck!