The first step is solid oral narration experience. Has she mastered oral narration? If not, continue with that until she's proficient in it.
If she's good to go with oral narration, an easy way to start the transition to written is to write or type her narration as she speaks it. Then when she's winding down and nearly done, step aside and have her finish writing or typing. As she gets comfortable with that step, begin to step aside earlier and earlier until she's writing the whole thing herself.
For beginning written narrations, be sure to encourage rather than critique. Wait until she is comfortable getting her thoughts onto paper before you start correcting things. And when you do start, select just one or two points to focus on at a time, rather than "bleeding" all over her paper.
I hope these ideas help some.