My puppy fell ill suddenly in 2012, too and I knew if I didn't take her to the vet to put her down she would have suffered severely for a few more hours and would not have made it through the night.
The cat I lost last year, Jim...had I had access to the money I would have spent it on his surgery in a heartbeat, so I totally understand you spending what you could on her.
Unfortunately for me, I decided to give him up to my vet who said that she might be able to find a caretaker to accept him and pay for his surgery so he could live a full life (he was 5) even if it wasn't with me. After a few days of being inconsolable, I went back to my vet to ask to take him home again because I was his entire life and he had a horrible life before me. I don't know what actually happened to him, but he had signs of physical scars in his black fur and he had serious psychological issues. Even if he was destined to die in my care, at least he would have me to the end and know that I loved him. When I got to my vet, she said she couldn't find anyone and he passed earlier that day.
He died thinking that I abandoned him after giving him so much hope.