I rescued a feral cat a three of years ago, she was sick, very sick, thin and weak. She was diagnosed with non-regenrative anemia. The vet also did a bone marrow sample to test it and they confirmed that the anemia couldn't be fixed. They proposed the euthanasia for the cat, because she was declining and unrecoverable.One of the vets did recommend euthanasia right from the start when we discovered Baby had non-regenerative anemia, but I was not open to that at that time without knowing what condition Baby had. Though we still don’t have a diagnosis, if there isn’t a cure for her condition, I’m open to euthanasia.
I told them I was agianst it, and that they should have tried harder, whatever they could do.
And they did, and with a long therapy with just prednisolone (a really inexpensive drug) for several months, the cat fully recovered, and now she's a wonderful healthy cat... alive!
I have the feeling that vets tend to suggest the euthanasia very easily when they have to deal with feral or stray cats.
You say that SDMA is high, but the other renal values are ok. I think that SDMA overrules the other levels, so I believe that Baby has a renal condition, and this could explain the anemia too, along with a bone marrow issue.
My advice is to keep caring for Baby as long as she feels quite well, and still eats and loves you.
When time comes, she will let you know.
You're doing a wonderful job!