I am not saying Asmode is a God or can control a person down to the minute detail. She is doing things based on human ego and human personalities. Asmodeus read MC’s mind and knew all the parties involved and what happened through reading MC’s mind.
She knew what they would do based on the human ego after being deprived of food and water for three days.
Yes she knew what Miku would do based on what Miku was forced to do because of the bullies (thanks to MC’s memories, Miku’s personality, the personality of those bullies with her and what those personalities would do in a food deprived situation where they are forced to depend solely on MC for anything. The only things they had to offer MC in exchange to get better treatment/food in the holding cell are their bodies.
Asmodeus chose MC because she suspected he was very likely to become highly suitable for the role she gave him, and told him to do what he wanted with his new powers in punishing those that had done him wrong, then let him steer the wheel without back-seat driving.
Asmodeus didn't tell him who to kidnap or who not to kidnap, because that would not be giving him full control, so the three girls he kidnapped were kidnapped entirely by his own will and doing, Asmodeus wasn't involved in this beyond, perhaps, teaching him how to control the room creation power before the kidnapping happened, but nothing else than that.
After the kidnappings, the only time Asmodeus chimed in was to remind MC that he needed to provide food and water to the prisoners, otherwise they would die, but this was only done because she figured he had thought movie logic was real logic, in which people could survive without food and water for an entire week straight. Then it was still MC behind the steering wheel, with no back-seat driving done by Asmodeus, nor any sneaky mind-controlling of the prisoners by Asmodeus, Asmodeus was just a spectator enjoying the show, not doing anything to intervene in MC's plans.
In other words, Miku realized on her own that she could get better treatment from MC by sexually servicing him and devoting herself to him, because Asmodeus was still only spectating things even at this point, and had not done anything to prompt Miku to do what she did.
It wasn't until at this point, where the MC's lack of sexual experience caused him to falter, that Asmodeus finally started sharing control over the steering wheel with MC, first by teaching him sexually with her servant, then by providing him the costume and throne and telling him what to do with them and Miku to bring forth what Asmodeus had suspected - from her spectating - lie within Miku.
In short, Miku herself, controlled by no one else, and of her own free will, sexually serviced MC and devoted herself to him because she figured it would likely give her better treatment.