Jill is definitely going to develop, we can see that quite clearly from some of her reactions to the MC's actions that have been brought up already, and the fact that Bella is pushing her to grow up as well. Whether it's the MC's actions, Bella's advice, or Tybalt being creepy to her, Jill's naivety will eventually press up against reality and force her to change.
The big problem with her character in general, though, is that she's an archetypal 'virginal princess' character in a sex game. All of her solo scenes, meaning those that aren't grounded by Bella's more mature and sexualized character, are a complete tonal shift to the game. That's why I find Jill's scenes thus far to be pretty disappointing - you can pretty much predict at the start of a Jill scene that there's going to be no progress for the characters and relationship, and be vindicated five minutes later. This kind of relationship is the very definition of 'slowburn', which isn't a bad thing normally, but it's not being paced correctly in comparison with the other LI's and the MC's own personal development. We meet Jill in episode 1, it's episode 7 now and in that time the MC has joined a frat, passed all its trials and become its de facto leader, struggled with personal issues surrounding his mother and her diary, developed emotionally, mentally and physically, and has actually competed for Jill's affection if he's on her path. In the same amount of time, Jill has practically not developed at all, she's just sitting there like a prize to be claimed - which, again, fits her archetype perfectly, but it's not compelling in a story full of other compelling characters.
The good news is Jill is definitely going to develop. But depending on how long this game is, I think we're roughly at the 50% mark after next episode, there's little doubt that her interesting content is going to be back-loaded heavily. This is a shame because DPC could have easily sped up Jill's progression to match Bella's, and I've often thought that those two characters should be more closely linked like Josy and Maya are. I don't know if we'll ever get the fabled Jill/Bella threesome, but Jill and Bella are so closely linked in each other's character development that it's actually pretty jarring that we get a scene where Bella takes off her wedding ring but the best we get with Jill is her masturbating while thinking all romance should be some fairy tale shit

Like bitch, you know more about how Bella's marriage ended than any other character in the story, your best friend is direct testimony that real relationships can involve incredible amounts of pain. The way Jill ignores all of Bella's warnings is probably the most frustrating thing in the story I can think of.