This, in case you can't tell, is Sunshine's bowl. When I left the house in the morning, I filled it with water. By the time I came back, she filled it with dirt. Judging by the fact that most of dirt was wet, there was still water in the bowl when she started digging. The same happened to her food bowl once or twice before.
She started doing it about a month ago, and we have no clue why.
And here is Sunshine herself: