I think these have to be quite specific i.e. remove hidden maid trait etc But I do remember them being tied to a mod which exposes the hidden 'traits'. I had a quick look on twisted Mexis reddit page but couldn't see anything. That doesn't mean the info isn't out there somewhere @FrancescaFiori just means I'm not 100% sure where to look!
I hear you on the story-line being altered because of this. That gets me every time. I have so many unfinished stories due to not being able to get the sims to do what I had envisaged for the story. 
Good luck with the rest of your ID... so close now. 
Yea I use a MTS mod called "Add More CAS Traits" that has an optional mod to add and remove traits in game. I hesitate to post a link to it here since it's relatively outdated. <Not updated since end of April> But the two modules I have installed still seem to work ok for me.
In any case it shows alot of the "Hidden" traits also like custom gender, if the sim is insane, their walk style....etc....and it shows the hidden one for "Flag Never Marry" so probably somehow her sim got that trait on it. HOW it got on to the sim is a whole other bundle of beans. LOL Sounds like it was more related to the Serial Romantic aspiration than being flagged as a Butler, but then again who knows.
It could be some kind of wonky flagging that happened after the last patch or when she got the VG Stuff.
In any case i'm glad you found a workaround for it somewhere
@FrancescaFiori Alot of people spend half their time digging into the game files after patches and new content comes out and I figured someone would eventually find something similar enough to your problem and post about it.
