Jill seems so much more pugnacious with her put downs than we've come to expect from her. We don't see the level of naivety that she displays later on with Tybalt. It's almost as if she has become less confident and secure since her first year instead of more. I'd really like to know what she has got up to at B&R for the previous couple years before MC arrived.

What happened in the interim? Because back then she's zinging one-liners, going on dates, sleep humping school librarians, and generally just swagging around campus like a boss. And who is her friend?
Since we've got the two best examples of Jill's changing look in your posts, I might as well point it out. Itty bitty titty intro Jill overall looks fantastic except for the teeth per usual. Nice skin tone, clear eyes, still has the killer quads. Fast forward a few episodes and we have pale, glassy-eyed, wrinkly-faced, 40-yr old bloated Jill who looks like she's headed to the ladies' room to catch up on a coke rail with Quinn's mom.