I'm so sorry you're having to deal with this.
For what it's worth, that would be my approach as well. My mother's 13 year old springer/cocker cross was diagnosed with lymphoma and we just made her comfortable; we knew she still felt a little bit okay when she perked up at the site of pizza boxes and the prospect of a whole lot of crust for her.
And at her age, we also felt like we didn't want to do anything drastic.
I'm going through this with my own 15 year old lab mix right now. He has such terrible arthritis (in his limbs and we think his spine) and has doggie alzheimers. For the first time in his life, he didn't want to go on a walk the other day, and today, my husband got home to find him stuck under the bed having panicked and messed all over himself. And when we have days like that, I remember how really old he is. But then, he follows me around the house with a big stupid labby grin on his face and I know he's still happy. I think he even enjoyed the bath he got when I got home, which is pretty unusual. I do everything I can to make him happy and comfortable. But I do find myself wondering why I bother asking the vet about things. He had a growth on his side that looked different from his usual sebaceous gland cysts that he has all over him now, and I almost didn't ask about it because, even if it was something like cancer, he's not in shape enough to go through anything other than steroids to keep him comfortable.
We've been lucky to have him around this long-- I've had him for officially half of my life now.
As long as he can be comfortable, happy, still smile when he sees me coming and can get up without me doing too much more than giving him a little extra lift on the back end, then life is good.
Long story short? I would do, and basically am doing, what you're doing. At some point, the tests and treatment are worse than the disease.
It sucks having to make decisions for our animals, sometimes. Hopefully acupuncture and the meds will make her comfy.
"In these bodies, we will live; in these bodies we will die.
Where you invest your love, you invest your life." --Marcus Mumford