Agreed. Also, while I think many of the younger actors have grown into their roles, I feel like you can really see the most development with XM's line deliveries and emoting than the others.
On another note, Ali first mentions to Johnny that she and her husband are separated, but later in the same conversation says her parents are mad at her about "the whole divorce thing." Even later (following episode) she mentions to Daniel that it's just Mills now, no Schwarber. Almost all the pictures we see on her FB page are also of her alone, or occasionally with her kids (no hubby).
My takeaway is that she is actually divorced now, and not just separated. It's possible that the writers just used those terms interchangeably in her dialogue with Johnny, without regard to the fact that they have very different meanings/implications (as any child of separated or divorced parents would know). I hope that they were actually doing this intentionally, though; maybe Ali was initially nervous about being forthcoming about the extent of her marriage situation, but later became more comfortable with Johnny. He didn't seem to have much reaction at the different terminology, though. It's possible that the writers may also be hedging their bets here, setting up a storyline for a possible love triangle with Johnny-Carmen-and-Ali if they can get Elisabeth Shue back for a few more episodes in S4.