I could not go through her sub path even using a multi-mod as a second option cause she is a baby with puppy's eyes in a fully developed hot body.
Like you, I initially wanted to go back and make a save where I could turn Vess into my "servant", once I saw that option mentioned in the walkthrough. However, I just couldn't follow through with it either. The whole "treating her badly" thing just feels...wrong, once you become close to her. You know, expanding on that thought, I think her love/romance path might have a bit of a missed opportunity in how it's been implemented. Perhaps something could be added like: Vess offers to "repay the trust" of the MC with some kinky sex, and then gets embarrassed and admits it excites her to try out her fantasy of being treated like a "captured spy" by him. IMO Vess was just born to role play a submissive sex slave in the bedroom, and it's a shame that you have to kind of be an asshole just to see that unfold.
Now that particular scenario I suggest likely won't work with what the dev has planned for the rest of the game, but a man can dream, right?
![Stick out tongue :p :p](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
Still, I would definitely enjoy seeing some extra focus on Vess' romance path, in whatever way is possible and fits in with the planned story.