Sorry to reply again, but what would you think then of a kind of battle of wits ? I guess you would want anyway Marc to win it (or maybe not, depending on the choices).
Something like, Katherine clearly wants to protect her mom, Marc wants to get her (and Katherine) under him, the to kind of fight (but not in a direct hands to hands combat, of course).
But it could end up with a kind of battle over more than one scene, where Marc tries to get the mom under his control, Katherine tries to battle it to help break free.
But even if Katherine she is successful, she may end up being anyway only end up putting the mom sexually under her, "share" her (though that for Marc would be a defeat), really help her get free (from Marc and Anthony, if she has not yet kicked him out).
And she could lose her mom to Marc (and Anthony, if still around), lose herself and mom to Marc and Anthony, etc...
Plus there is to be seen how Evelyn, Jennifer, the psychologist (actually, is the reason in theory psychanalists are forbidden from having relations with their patients, and anybody doing psychological support is told to be careful, it is easy for the subject to develop a form of emotional dependency or what may seem even to them feelings), William, the director, the professor, the policemen, etc. would enter influence the situation or make it completely different.