I've been looking all over for any signs. The yard is fenced, and like I said, not that big. No sign of the bowl, no sign of broken glass. The one bird I found was under a papasan cushion that I have next to the garbage cans to throw out. I have looked under every possible bit of cover in the yard, so I'm pretty sure my favourite hen is gone.Yikes.
Keep looking for the bowl or broken glass.
Do you have a fenced yard?

It has to have been a person, but... Why?!

I even have a 10' soundwall on the back part of the yard. The fences on either side are 8' rather than the standard 6', so if she left the yard voluntarily, it had to have been under the fence, and I don't see anywhere that she could fit under it.