I am so sorry for your loss. I think everyone manages to feel guilt, whether a pet dies on its own or whether everything technically goes "right" and a dog lives to a nice, ripe old age but then you still have to give the final go ahead to the vet to end your pet's life.
Time really is a healer. I'm not sure I believed that right after my dog died (at the beginning of Dec -- she was 15 years old), but that gut-wrenching awfulness doesn't last forever. Everyone has their own timeline. I didn't feel as despondent at two weeks out (I still cried everyday but I no longer felt like my life might be ruined forever), and now, a couple of months later, I'm ok. I miss her and feel badly because I go for longer periods of time without thinking about her, but I am happy to be able to enjoy life and stop obsessing and feeling constantly sad. So hang in there.
I'm glad you had a memorial for her.
Thank you, Im sorry for our loss also and im happy that you are doing better and able to be happy. I hope I can get there one day