Is her writing well-organized, with each paragraph being its own topic with topic sentence (generally speaking)? If yes, it sounds like she is right on track, and I agree with Melanie32, that I would just have her continue writing narrations. I’m not sure if you are doing this, but you can “focus” them, or give her a topic to write about, instead of just retelling what she’s read. Like, ask her to compare two people, or give her opinion on a decision a character made, etc.
Beyond that, I will tell you that with my 9th grade son, his writing isn’t “deep” or mature, because he isn’t deep or mature… yet. Sometimes I think he should be writing more academically, but he just lacks the maturity right now. You can only write about what you know, and what you think, and if you think immaturely, as 8th-9th graders are apt to, then they will write that way. If I give him a topic that he doesn’t think much about, he just can’t write about it. Earlier this year I wanted him to write about a question from Notgrass history, which was something like, “If you don’t believe in a Creator, how will that affect the way you live your life?” And he had just NEVER thought about that before, so he was at a total loss. We had a conversation about it, and he wrote about something else. But my point is, try not to expect more maturity or depth in her writing than where she is in life right now.
Don’t worry, we have four years of high school to get them where we think they should be. 🙂