I know the dev said permanently losing Nikki or whatever is a side effect of treating her badly as people won't stick around for that (and other LIs will be lost too) as the MC isn't an evil genius just rich and can kinda read people so there's no way he'd pull off anything wildly beyond the bounds of reason... but I think Isabella (that's Brit's mum's name right?) would make for the perfect dark playthrough partner. Not being a dick to her personally, but I feel like she'd happily stick around and assist with whatever horrid things the MC wants to do to all the girls if it got her the good life, especially as he's not like he's some wrinkled old pensioner (which it sorta sounds like she's used to). Kinda like how the MC made Nikki join in with the Britt photoshoot, but here Isabella would be a willing participant. I could totally see her also being useful to put on this like clean, wholesome wifey façade to throw the heat off if the MC ever gets accused of stuff. Hell, maybe even starting a tandem charity for destitute girls / women's shelter kinda deal... and then making use of the most vulnerable there. Not that I expect the dev to take it that far, but I just think she'd make for the perfect ruthless wifey here.
TL;DR: We'll lose multiple girls due to dark choices, so I think Brit's mother could be a dark only permeant companion counterbalance to that.