I so sorry for your loss and pain.
You miss her so much because you love her so much.
Our first pup has this terrible illness, it was so painful to watch.
I know I did the right thing because she had stopped eating from my hand, and for other reasons, it was time.
It really takes time (and kindness from folk) to help heal you, and it will always hurt, but it may not tear you apart. You will remember the joyful and beautiful and funny moments.
It has been several years, so, I hope you are doing better in this regard.
(And I did want to die for one day, afterwards. I was feeling utterly devastated lost and alone.)