The thing is that I recently made a new playthrough and I obviously went for Jill since she is my favorite and the thing is, Jill is in no way a prude. It's easier to notice this if you make a direct playthrough from start to finish.
She is prudish yes, but Jill is a nearly identical mirror to her sister, both looks and personality wise and she loves when she feels that she is mirroring Lana's behaviour.
So the reason for her to be prudish is because of her parents and her being with the MC and also being betrayed by Bella helped wake some of her hidden self. In this episode Jill is the one coming on the MC basically all of the time and not the opposite, teasing him, inviting him to 'fuck her' in a public space out of the blue (that was so hot that my dick grew another inch, I understand that line of the MC a lot better now).
And also, the revelation that Jill was the one to start the make out session with Bella and she was also the one that asked Bianca to kiss her.
Seeing those interactions and how much Jill has developed makes me think that it's not difficult for her to actually start a threeway relationship with either Bella or Bianca some time soon and maybe even more than just that. This is just the surface of who Jill actually is if she stopped caring what others thought of her and embraced what made her feel good.