Hello, my name is Dr. Kara and I have over 20 years of experience as a veterinarian.
I'm sorry to hear that Sasha is having so much trouble eating.
It sounds like she is experiencing pain when she is eating which causes her to paw at her face.
This discomfort can be from an infected tooth (teeth), gum disease, a mass or a foreign body caught between her teeth, in her gums, tonsils, behind her soft palate, or the roof of her mouth, under her tongue or even in her esophagus.
Because she is able to drink, is drinking a normal amount of water and wants to eat I don't believe that her discomfort is related to organ failure and secondary erosions in her mouth or gastrointestinal tract but that is a remote possibility given her age.
I think she needs a thorough veterinary examination including sedation to look up behind her soft palate, down into her throat and under her tongue thoroughly and possibly some radiographs of her skull and chest.
In the meantime I recommend blenderizing cat food with some warm chicken broth so she is able to get appropriate nutrition. Try offering food several times a day so even if she can't eat much at once she can still take in enough calories.
Please let me know if you have any further questions.