I'm seeing it like this:
She's vital to the plot as both a counterbalance to Bob's plotline and, very likely, the story's biggest plot twist (or a subversion of said plot twist). Now, what power can possibly drive the MC away from his longtime friend? Why, he's going through midlife crisis, becomes all sentimental and gets into a honey trap of course! Why do we need points though? They will probably decide MC's reaction when we find out the truth about her. Will we win her through Power of Love, dominate her through sex, or will she successfully betray us, forcing us to rely on Bob for help? Up to us!
So I'd say we're not actually on Emily's path yet, unlike how it may seem, as all of their flirting is just part of main story, and we can still lose her to the villains. The moment it's possible but we don't is when her path actually starts, and for that, choices will be important.
You are right Zorro, and if I think about it rationally I know it, heck I even said I was sure she was really intended to be the daughter (pre-rework), and I know we are playing an AVN, so the sexual sphere should be relevant, but...
Since she can't be the daughter (anymore?), so there's no "big plot twist" concerning her, besides the fact that she's an honey trap and onto something, everything you said could be achieved without the need to force the MC to "fall for her".
- He could keep her around because he trusts her, thou it should have been shown better
- He could keep her around because she works well, thou they actually never show anything remotely close (besides her saying she does it and hi saying "yes baby... gimme that ass tho!")
- He could have kept her around because they actually start a friendship, which is clearly not intended in-game.
She's a trope that I always tend to find "off-putting", even when it's done better (e.g. Elsa in that abandoned game), if I want to be rational, rather than just "whining" about an LI I dislike, that's the crux of it all, she could have been written better.
She really has no redeeming quality, meaning we don't see it besides her telling us how good she is and the MC nodding while drooling, except for being hot, hot in a setting where every single woman around a succesfull, ruthless, and self-made "womanizer" MC, is a hottie.
Using the example above, Elsa is actually smarter than that MC, she knows it, he knows it, she clearly had her own agenda, but we as players were left wondering if it was a nafarious one, or simply that she likes to help bumbling buffoons to succeed, etc...
Sorry went for another of my lentghy rants, the TL;DL is:
This is of course all personal opinion, I tend not to like forced LIs, but since I know in some cases they are integral to the storyline, I wish they'd at least been written better, this isn't a kinetic novel there are a lot of ways (that don't take much extra work/variables) to allow for her to remain a vital part of the storyline even without being a forced LI.