I don't know what you mean? Her being oblivious to so much, is almost her core character trait. It's hard to say just one thing, when it's the core of so much of what she chooses to do. A lot of her naivety is in display with conversations with Bella.
Also one scene that comes to mind is on the MC's first date, Jill talks about having to have sex on the 3rd date, almost like it's mandatory. Like I compared before, that's something like an Android first built would believe.
I'm not hating on Jill btw, I actually like her, but part of her being so naive about stuff is kinda to unrealistic. I feel like she's an Amish teenager lol.