How can we ease pain from a dog who has cancer?

My boyfriend and I have been housesitting for the past 2 weeks for his mom who is in Europe. A week and a half ago we noticed she wasnt eating and thought she could just be depressed. After a few days of barely eating and drinking a ton of water, we thought something is wrong and took her to a vet. $900 later we found out that she "most likely" has cancer in her spleen, liver, kidneys and a mass in her abdomen. I say most likely because her ultrasound shows thee type of nodules that are present, the way they look, are suspicious of cancer. They wanted $400 more to do the biopsy. She is 11 and weak with IMHA and needs also a blood transfusion. Doc doesnt think she will make it through. She is not eating still and now not drinking any water and barely able to go outside. She is however very active at night pacing while we are sleeping and dont know why that is. 

The family is a mess and Im trying to help out in any way. What advice do you have to help ease "Lella's" pain? I know putting her to sleep is next but we are so torn in doing that because his mom is out of the country, she is having a hard time letting go without saying goodbye....this has been so difficult. I want to give the poor dog something to help her in the meantime and he and his mom are not thinking clearly. 

 Ask your boyfriend to call his mom NOW and ask her "do we really want to let Lellas's pain continue until you can come home?" 

It would be selfish of her to do so. I recently had to put my 14 year old friend down (Siberian Husky). My only regret is that I allowed her pain to linger two or three days longer than I should have. 

If the vet says that treatment WILL prolong life and make her more comfortable maybe worth a try. I doubt the vet will give any sort of hope such as that though.