Dang. I thought you guys would jump all over this one.
I'm guessing the thing has never been saddled and has been nothing more than a pasture ornament. It's too small to ride at any rate.
I've heard that some donkeys can make decent guard animals, but I've never heard of a guard mule. It's been gelded, but at what age? I'm guessing that it was after it was rescued and nobody's told the mule that yet.
You're right about one thing - the price. Does that mean she'll pay me $400 to take it off her hands? $200 should be enough to rent a backhoe or hire 4 Mexicans to give it a decent burial.