Whenever a porn game has a character like Isabella, someone who is legitimately just a nasty person and hurts the people around her, my inner sadist kicks in. Basically I wouldn't be happy with any scene involving Isabella that wasn't rough, mean, and humiliating for her.
On the good path that could be something like, after you secure a high-paying acting gig for Brittani, she cuts her mother out of her life. Isabella comes to you asking for support, either monetary or to win Brittani back. She expects to pay you with sex, because she really believes malexfemale relationships can only ever be transactional, a zero-sum game. You can either rebuff her, which she'd take poorly, or you can fuck her. She'd be down for anything (she's been in this position before) but there would be a lot of eye-rolling and she'd be bored for most of it... unless you made her pay attention with rough stuff. This kind of steps on the story beats that Risa has but I'm just spitballing.
On the evil path I'm thinking of a scene where Brittani is doing a modelling shoot for you, and Isabella is there making a shit-ton of demands, and being annoying. Of course she's aware that you're an asshole, but she feels a bit too comfortable thinking that, as a fellow asshole, you have a kinship. She believes there's a hierarchy where she's only slightly below you, since she controls her daughter's labor, which you want. Eventually she pushes too hard and ruins the shoot, and you take out your anger on her violently and in front of her daughter. I mean completely overpower her, really destroy both Isabella's bad bitch self-image and any belief Brittani has that her mom deserves respect. In fact, put Isabella and Brittani, mother and daughter on the same level: whore who's there to please you.
I also want to do this with that brunette girl that hangs out with Jamie. God she sucks.