I add my voice to all the other ones who told you not to think for a minute that you are a horrible person. If we are always saying that any decisions we make should be for the welfare of our pets, you are the one who knows now it's time to let her go on her way to the Rainbow Bridge because you love her.
You made the last year of her life a happy one, and while she plays, without any more pain, at the Bridge she'll remember that.
I had to make the same decision for my first Golden because her cancer had taken over her body and I could not stay with her either. I was alone and was afraid the vet would have to pick me up from the floor if I'd stayed.
I'll be thinking of you and sending many loving thoughts your way.
Have a safe trip, darling Peka...