Sorry I missed your earlier reply.
Sasha should stay away from too much protein and foods high in phosphorus. I wouldn't recommend beef liver or yogurt. Beef liver is not a lean protein and yogurt can give some dogs diarrhea because it contains lactose as well as both being foods high in phosphorus. Organ meats in general are high in phosphoru. Phosphorus nis an electrolyte that failing kidneys have difficulty removing. If the blood levels of phosphorus are too high calcium is leached from the bones leading to weak bones and calcification of the kidneys.
Tomatoes are fine however they are highly acidic and many dogs with kidney failure have gastrointestinal irritation/ulceration because of the effects of kidney waste products on the gastrointestinal tract.
As far as beneficial treatments fluid therapy to keep kidney waste products at a low level by flushing them out is often beneficial. Usually we start with intravenous therapy at the veterinary clinic then use subcutaneous fluids long term to manage the levels. You can learn to do this at home.
I also recommend a phosphate binder if her blood levels of phosphorus are too high.
If she isn't eating well sucralfate, a coating medication, can help heal gastrointestinal ulcers which will improve her appetite.
Acid reducers to try and settle her stomach are also useful. Either:
1) Pepcid-ac (famotidine) at one 10mg tablet per 20 to 40 pounds of body weight every 12 hours.
2) Prilosec (omeprazole) at one 10mg tablet per 20 to 40 pounds of body weight every 24 hours.
These medications are quite safe and can be used for several days if necessary or for as long as necessary.
I also recommend an omega 3 fatty acid. These are natural anti-inflammatories and have been proven helpful in dogs with kidney disease. Reputable brands are 3V Caps and Derm Caps.
Additional testing that should be done is a culture and sensitivity of her urine to check for infection. Infections will worsen kidney failure and in some cases are the cause. Treating the infection can get the waste product levels back inti the normal range in some cases.
If she is clear for an infection then checking a urine protein/creatinine ratio is recommended. If she is spilling more protein then creatinine proportionally then she should be put on a meduction to help decrease protein loss. Protein loss leads to weight loss and worsening disease. Enalapril or Benezapril are commonly used medications for this.
Her blood pressure should be checked as well. Many dogs with kidney failure have secondary hypertension and this damages the kidneys further. If her blood pressure is elevated then Benezapril is the drug of choice for treatment.
Finally if bringing down her waste product levels and controlling stomach upset and hypertension isn't enough to keep her appetite we can use appetite stimulants. Dogs that eat and maintain body weight are proven to do better in the long run. Mirtazapine or cyproheptadine are both worth trying. They have different mechanisms of action so if one doesn't work try the other.
I hope this information gives you a place to start. Good luck with your girl and let me know if you have any further questions.