Sorry if that got a bit dark, but I've been playing Coffin of Andy and Leyley and can't help but reminded of that when I refresh my memories on past chapters.Were this was the past momo, it would absolutely be on the table. Hence her sexual harassment (if not outright assault) on him during the Spring vacation arc.
But she's aware that should she pull this off, she'll just end up with an actual toy, lifeless husk of a human being, a Ryuju's whore. She could win the body, but at the cost of his mind.
It's cute that Momo's becoming more feminine and understanding concept like empathy and remorse, but ultimately those are just trappings of humanity she puts up to make Hachiman likes her. Her core is still as twisted as anyone groomed to be the head of a large criminal organization would be, and I was kinda hoping she'd say or imply something fucked up off-handedly just so the rest of the cast understood that they shouldn't go about poking this particular hornet's nest.
But I guess it's nice to think that she shows that level of restraint because she cares about people Hachiman cares about, even if she doesn't particularly likes them being her romantic rival.