Yeah, structuring a one-off for her, featuring Lemon Zest and Vinyl now. But, it's possible to have Zest be the bimbo at the end of this part, and just start on Octavia. Call it a moment of regret on Vinyl's part that she cuts short the session leaving Octavia addled, but still mostly herself. Or just leave Octavia alone altogether and give her an inkling that something's wrong.
Octavia recognizing that something is wrong with Vinyl, and questioning if the relationship between them is still what she remembers, might be the twist of the knife this next part's been lacking. It could also lead up to a nice changes of pace where there's a willingness to succumb, as willing as you can be at CHS anyway.
Looking back, there might have been a better collection for the counter-team, but this one feels hodge-podge enough to express the urgency of what's going on. They'll do well enough for what they're roles is, even if I'm not the biggest fan of some of them.
As far as writing goes, it's a little hard to find things left to do in the demo when it comes to story-related content. Off the top of my head, outside of the transformation, lewds, and ten more S-Links, there isn't too much meaty content left. I guess we need to decide if Cheerilee and Pinkie (possibly Velvet?) are getting their TF's written out as well, or if it's just a mechanic for them at this point.
With that in mind, you're probably on the right track with looking at general interactions for either of those three. There's also the thought of making the Cafeteria/Sugar Cube Corner a place where you can listen in on what people currently think about Twilight (or any of the students/staff), so if it were possible to do that then that could be two to five text boxes worth of content that could be done for a variety of instances (Twilight Studying/slutty outfit, Miss Cheerilee's homework/short skirt, Pinkie's last party/rumors). It's yet another thing to code for, but it would add depth to the world.