I am so sorry she is unwell like this. I agree you should follow your vet's advice for her. But do mention "Milk Thistle" to your vet as this herb can help support liver function and is widely used for dogs. You could buy a glycerin tincture of Milk Thistle (from a reputable company online) Or tablets which can be sprinkled on her food.
It is not a miracle, but might help support her liver function.
I do understand how you feel about your girl. My dog passed from Hemangiosarcoma in 2012 and she was also 'all I had'. I was brave enough to let her go when her time arrived to leave the Earth, but miss her deeply and always will so long as I live. She was (and still is -although now in Spirit!) -a very wonderful friend.
Very sorry to read of your grief.
There is a lot of expertise on this board (forum/community) and as I see your post at the bottom of page one it seems there are no suggestions beyond what you are doing.
All I can suggest is follow what he veterinarian tells you and try to make you dog as comfortable as you can.
When we lost our little Westie due to an intestinal tumor rupture we went to the dog shelter and picked up Jasper, a mixed breed Pomchi I call it. That way the loss of Wilson gave a needed dog a home. Both Wilson and Jasper are in my picture gallery. Both were/are small, under 20 pounds.
It is very hard to let go, but if it comes to that please consider what is best for the dog. To me, pain without hope is something I'd not put a dog through. This was the case with Wilson mentioned above.