Someone has been a very naughty girl and now extreme measures must be taken for her own good. Her master has no other choice but to work his body modification magic between her legs, since she simply cannot be trusted to not be caught acting like a silly little slut.
Of course, this is something that needs doing for HER sake. Not his. Therefore, it won't be free. On the contrary, it will come at a price that any whore would be happy to pay.
Afterwards, she can be thrown back to the wolves like the piece of meat she is and loves being.