I'm so sorry for the grief you must go through. It is so very hard. I know how you loved your Ella and what a happy life she had with you. Sometimes it's hard to know why we put ourselves through this time after time. And for most of us, we find the answer that has to do with our most phenomenal bond of love we have with our dogs.
It's been a couple years now, since I lost my Doberman, Lyric. And I never stop missing him. I get little flash backs of cute things he did or things in my environment that remind me of something....always happy thoughts now. The sharpness of the pain has gone. And lots of good memories have replaced that stabbing pain.
It's so hard for a long time because it's like they're there with you on the one hand and then you realize they're not....physically. It's like they're made up of two parts: The spiritual part that stays in your heart...and the physical part. I remember the confusion that would fill every ounce of me....is he here or is he gone? Not intellectually, of course. I knew he was gone. But was he? I wrote poems about this feeling....as an outlet. ("are you here or are you there, it's hardly plain to me") I dug into my deepest part of me to try an analyze my emotions or maybe not analyze, but to get in touch with them and writing seemed to spell it all out better for me. I hope you can find some way to help you through your grief, the confusion, the unfairness of it all. Every part of it has to be touched and felt, looked at in order to wade through the heaviness of the long road.
Right now, probably none of that makes sense, but it might later. I'm so sorry for your pain. But know that you did the right thing for Ella, that she is free of pain and anguish. You have taken that pain onto yourselves so she could be free. You've done the best for her up through the end. Soon, let her memory of all the good times heal you. That will, in time give you acceptance which will set you free. ((((HUGS))))