At least one tooth is definitely killing my dog, but the vet does not want to proceed. If I do nothing, she is near the end.?

I was given my family dog jan 2017, but knew she was going to need some extra tooth care. She began sneezing and had trouble breathing whenever she was excited, eating, or playing, so I took her in for some extractions. They refused, and wanted to send me home with new food for kidney disease, antibiotics, supplements, herbs, etc... That response killed me. I knew these things would not cure her problem, but I gave in desperately, I will admit, she was EXTREMELY HAPPY and seemingly healthy on antibiotics and new food, until she ran out of antibiotics. The sneezing came back, and her nasal breathing difficult. Now, her condition accelerated from the treatments and she only eats when shes starving. Awake, she struggles and... Okay, you get the point. We can't escape the end, but to put my dog down because of an infected tooth sounds absolutely insane. I'm giving her a few more days left.. I need to know if there is anything else I can do? It's too late for "brush her teeth" or "take her to the vet." "Don't take in a pet you can't take care of" is obviously inaccurate, I'm surely doing whatever I can.