Former middle school teacher here! I tutor many kids in writing, and I often see the situation you're describing. It sounds like she may not be reading with the writing in mind, so she's not sorting and retaining the information she needs when it comes time to put pen to paper. That leads to a hovering pen and not enough details.
If you're interested in learning more about my experience, you can reach out here:
jessica.leader@gmail.com.
Writing with middle-schoolers takes patience and skill. It's good that you're reaching out for support!