What a sweetie How wonderful that you gave her such a loving and caring home where she could enjoy being outside in the sun on soil and grass, under trees, loved and treated as a 'pet chicken' after her time in the battery That is what matters most - that she did have this wonderful time with you and because of you. Nothing can take this wonderful experience away - even not the way you two had to say goodbye to each otherAwful bedside manner!! So sorry that happened to you.
Thank you. Posting this, I didn't think anyone would understand why I was so upset to let her go. I imagined people thinking "it's just a chicken." It's quite validating to hear people say things like this, and it definitely makes it a little bit easier.
Anyway, I've attached a photo of her when I got her, and the most recent photo of her stealing my drink. She has been a pleasure to own. She was part of my first ever group of chickens and I will always remember her as the one that inspired me to do this forever.
Thank you everyone for your lovely replies. I'm not going to complain, the vet thought she was doing the right thing. I just won't let it happen again.