I think Jill does know what happened, but she doesn't feel like it's her place to tell the MC and she'd be right about that. Whatever the story is between Bella and James and whether Jill was involved in it, it's up to Bella to decide if/when she wants to tell the MC.
it could also lead to the MC discovering that the path towards Bella heart is free for him to ram it in! Girls play tricks like that! So if Jill is interested in the MC she is cleaning the house to try and lock him up!
I mean she knows the MC so if its fixable and the MC being such a white knight she can probably conclude that the less he knows the better are her chances!
Because come on how much time would the MC spend with Bella more then he already does if she needs help going to therapy and then the decompressing times where you go for ice cream afterwards? Jill is a dumb Inbreed but far more cunning then what people give her credit for! Even the Tybalt problem is probably her playing on the MC white Knight nature to get a response out of him, cunning cunning raccoon eyes!
She already met Josy and probably bleed her dry for information (that he is a responsible and effective worker at least)!
So she is reading the battle terrain and accessing her "opponents" and using her assets! Since the MC does not seem to value money and she is not willing to give it up so easily she is fishing for all the advantages she can get! Tybalt is probably just another asset she can play to outsmart the MC into action!
Also the image you showed where she is surprised you where in her room! jealousy much? Put out or get out racoon!
Basically Jill doesn't know that Mc may or may not have a romantic interest in Bella, so it's basically none of MC's business.
Then it depends on what this "secret" is and if Jill really knows it.
Surely Jill knows about the problems between Bella and her husband, but it's not certain that she really knows the cause of them.
After MC tells her about the locked room, Jill goes to check it, as if she wasn't quite sure what was supposed to be there. she probably has suspicions but I don't think she's sure.
the room only became locked after the 1st MC visit! so its either her waifupillow her sybian or personal shit that would create issues in her relationship with the MC such as she already being a mother or her ex-husband being a navy seal (you know the typical shit that makes men run for the hills)!
That could very well be but it would seem kind of odd considering there are definitely people who dislike Jade.
See: Roberts, Isabella
but why? Jade as the wealthiest husband... her position is higher in the college! There is nothing about Bella that can threaten Jade, that is why she is ok with a threesome!
Try and get your girl to set up a threesome with a girl that is more beautifull (or she assumes she is... because women ...) then she is and see her freak out! If its with a fatty or ugly no problem, just do not come inside of the fattie!