I'm sorry to hear that it wasn't good news.
I'm glad Junior has someone like you to love her. I'm sure she's well aware of how much you care. Sometimes, though it is the worst pain in the world, the best thing we can do is let our beloved pets know we are okay with them taking wing on a new kind of journey. I know it sounds a little crazy, but when Dovey passed, he had just had a seizure. He was looking so miserable and we rushed him to the ER vet, and all the time I held him in my hand instead of in the carrier in the car, just whispering to him that it was okay, that I understood he was suffering and if he needed to, he could go. I tried hard not to cry because when he was healthy, he would get very distraught if I cried and coo and coo. Somehow I do think that soothed him. As soon as they took him from me at the vet's, he went into cardiac arrest. I think in some way he was trying to comfort ME by not dying in my hand. He held on to make it easier for us.
I know Junior is far from you now, but even good thoughts...I'm not religious but I do believe energy is constant. She will feel the energy of your good thoughts for her. Energy is never created or destroyed. She just borrowed some for now, and if you let her know that you will always care and that this is "her choice" in a way, I think what will happen is what is meant to happen -- either she'll rally or she'll be thankful and move on.
You did everything you could. The rest is up to the vet and Junior.