She was in flashbacks, MC even tells Bella about her.
One way or the other, Zoey had and still has an effect over MC. Hell, she took his virginity.
Overall her interaction was alright in ep9. Things to note about Zoey in ep9:
1. The "chad" MC invites her, she doesn't force herself into his life.
2. She is fine with everyone, she calls out Derek a bit for being an idiot, but she's right. She makes a bit fun of Josy, which is also on point due to her infatuation with MC is transparent at this point, route or no route.
3. I enjoyed the Interlude and the fact that it shapes her differently going forward.
So Zoey is alright. In your place I'd be more worried about the MC? He's more retard in every episode.
I mean, he has a DEAD mom. He finally has a chance to know her more with the diary, yet he reads it one page per week. He's more retarded than Derek by now.
The "chad" MC is just a plot armored pussy at this point. Troy and Chad are more chads than him. I mean, ffs, MC chases pussy like a clown. Those 2 take dicks like real men.