Exactly, her teacher, whose name I forget, even told her to be ready to use her sex appeal. But that's different than having sex indiscreetly. Getting boned isn't a tool in a survival scenario, it's a loss in that scenario. That's what a woman who is trying to survive is trying to avoid. Shani isn't a sex starved nymph, she's been trained to be a badass, and is trying to survive in one piece. Her seducing someone and slitting their throat when they let their guard down to save herself would be within the bound of appropriateness. Her giving up, getting boned and then killing them or running off is essentially a failure state in this kind of game.
She strikes me as the kind of person who'd fight to the death before letting someone take her cherry (if she isn't with the MC) and would definitely never cheat on the MC if she is with him. Now, she might feign surrender to save herself, but that would end in one of her dozens of knifes in the enemy's neck long before they got near her prize.
Feel free to disagree of course, but from how I read her character, it would stretch credulity too far for her to have sex in the zone or afterwards for many reasons (not least of which is the nature of the zone itself). Except perhaps with the queen when she gets back, but then it's basically two members of a harem together so that'd be whatever.