Dump both buckets on her

Merry is screaming bloody ****. Threatening to kill you, to blow you, or to let you do anything to her, all in the same breath. It's too late though - your mind is already made up.

You slowly pour the first bucket of slop on her as she squeals like a pig, jiggling her breasts around as she struggles. Some members of the crowd are laughing so hard they're crying. For the second bucket, her scream is more muffled. I guess she learned her lesson about opening her mouth during something like this.

You spank her a couple times for good measure before you head back to the castle, leaving her naked and covered in manure, to the crowd's delight.