An interview session can't start out with the model's favorability bar showing a shield icon, if there is at start, then she will never want to have sex. To remove the shield from appearing at start, you need to fatigue the model, the more she is fatigued, the more willing she is to having sex or getting touched at places she didn't allow before. Once there is no shield on session start, then the next thing you need to do is to raise favorability to the max. If she still doesn't want to have sex, raise her arousal to max. If after all this she still doesn't want to have sex, then you need to raise her fatigue more. At 100% fatigue and max favorability and arousal, you are at the max threshold to have sex. You can possibly have sex with the model at 30%, 50%, or higher fatigue depending on the model. Some models only need favorability to be full while others need full favorability and some/a lot of arousal(like around 50%-60% arousal) to have sex. This is what the "horniness" personality score affects. Just so you know, high fatigue makes it harder to gain pleasure, arousal, and favorability.