You can add a bit of chicken broth or tuna water to her water and see if it entices her.
Also, maybe move the bowl or bucket to another location in the pen. Who knows, maybe she "thought" she saw something near the bowl that she didn't like. You know, like of of those "greyhound killer attack shadows!" :lol Danger is our spook and he has some "killer shadow" issues, among all his other issues. Anyway, we came back from a vacation and for the life of me, I could not get him to come in the garage after a potty romp. We would have to go outside and herd him in the door and he ran through it like a scalded chicken. After a lot of frustration on our part, I realized that our petsitter had moved a plastic chair so she could sit while the dogs were outside. He was freaked out about it. Weird dog. I guess my point is we never know what little thing may "bother" them.
I am not a "leave our dogs outside" person, but I know that Danger would stay outside if given the chance. I have to drag him inside now after 10 minutes in the yard. And Disco would stay out also. But Dicso would be too lazy to get up and drink. :rofl