It's the hardest thing to have the Vet euthanse your pet; it's hurts, and it grieves; but it's the kindest thing you can do, the last kindness you can give them, too.
Live long enough with pets and we all go through it, and it always hurts, and we miss them even years later. We live so long compared to them, but you gave her a good life while she shared yours, and you didn't leave her suffering in pain or confusion when life was not going to be good any longer.
I'm sorry you're both sore just now, I hope you both remember the good times, and the hurt eases.
Mary