I love the fantasy of taking a naked girl over my lap, explaining what she has done is wrong and that she will have to be punished.
The only thing I would add is a scratchy wool blanket over my legs so the wool would irritate her skin, especially her breasts and nipples as she squirmed. The spanking would be open handed and turn her cheeks bright pink/red from the top of her cheeks down to just above her knees; then a warm soapy enema, enough to make her squirm more and beg to be allowed to go to the toilet.
Keep her over the wool blanket and ask her if she wanted to be played with to take her mind off of the enema, slipping a hand under her mons and playing with her clit until she begged to be allowed to cum, and watching her struggle to hold the enema as you give her the final strokes with a finger to bring her off. then asking if she wants to go to the toilet.