Oh, yes. You are on the right track with this. Just think about Jill's lies regarding her stage fright. She says she has that, yet she also mentions she can easily do presentations in front of her class which consists of pretty much the same amount of students (as we can see during the business class scenes) as the audience in the auditorium does during the recital. You can easily conclude that this is either due to some kind of trauma that she has which she associates with playing the piano or playing the piano, but in front of other people. This is related to the Lana drama which is yet to unfold! It's no wonder she doesn't tell the MC about it and chooses to lie instead, similar to how she lied about wanting her first time of having sex to be perfect.
Remember the rejection scene with Jill? No? Well, then you never got it. Anyway, Jill rejects the MC for being a DIK regardless of whether he helped her during the recital or not. She even gets super-judgmental with the way she says "And you..." while pouting when the MC runs across the city all the way over to her. Jill is a manipulative woman. Very much so.
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You have to also understand that Jill is a character whose internal monologue is most of the time shown to us, but when is it not? Well, that's during her biggest bipolar moments when she drops the facade of being a pretty, young naive virgin girl and becomes completely emotionless and cold. There's a reason why these scenes are so long, yet they don't show us any kind of internal dialogue of hers. Usually such scenes in the game will still make the character's intentions clear, like Josy in Episode 10 when she tries reinventing her Rooster profile due to Oscar's insults towards her. Everything is made obvious about that and everyone knows that's what the scene was about. But with Jill? They look somewhat more like this:
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Look beyond her masquerade. You'll find the evident clues of her becoming the final villain of this game and betraying the MC. Watch her already be aware of who the MC's mother is and that the Royce property is the same house that was in the background in the picture of Tremolo's mother posing with her friends, who happen to also be Jill's friends' mothers (Bianca's and Carla's).