Oh Im so sorry to hear this news, it must be truely heartbreaking for you and I dont really know what else to say other that ((((huge hugs on the way for you))))
Oh my gosh... I'm so so sorry for you.
I was wondering all last night how you had got on with the vet, checking for an update post. elt sick when I saw this post.
I can't imagine how you must be feeling about the loss of the foal you've been looking forward too, but have been in exactly your shoes regarding her lameness.
When Cybele was diagnosed with bone spavins in both hocks, the beginning of serious coffin joint fusion and having done a tendon we were expecting that at the worst she's need her annular ligament snipped - after all we'd only called the vet out because we were concerned that her tenosynovitis wasn't improving, when all the time it had masked so many issues. I wouldn't wish that feeling on anyone, I felt winded.
We all know how much you love Amy, and whatever you decide it'll be because you know her so well, you won't make a wrong decision.
Big, big hugs. X