A dog or coyote (or any similar sized pred) can take an adult without a trace. Depending on where she was, the protection (fencing etc) that you have, she could have wandered off, gotten spooked or taken by a pred.
I have always found evidence of a kill. Once, all I found were 4 feathers, spread over about 200 yards along the pred's exit line, that was a coyote that took a young splash roo.
I hope you end up finding her, if not sorry for the loss. Do go out and shake your feed bucket or call them (I think everyone should aclimate their birds to a call).