So, I'm sitting here with my writing group tonight and we're all (supposed to be) critiquing manuscripts submitted to our fiction writing workshop, so I took a poll. Here's the group advice from several published fiction writers & semi-pros: don't worry about technique much. The best way to learn to write is to read, read, read and to write, write, write. She's smart: she'll learn through observation and practice. What she probably most needs is for you to be enthusiastic when she shares her work with you.
So maybe you might read what she's writing now and then and give some basic pointers (for example: in a good story, there's a series of difficult problems that the characters overcome in the climax; a story should have a beginning, a middle, and an ending; you shouldn't invent a bunch of characters you don't really need). Everybody here started writing as a kid, and nobody did much to intentionally develop technique until they were teenagers.
Also, the #1 thing a fiction writer needs is creativity. I have read many manuscripts that had all the technique in the world and were still incredibly boring stories.
At her age, you may be able to find some summer camps and extension classes focused on creative writing. You'll definitely be able to, when she's a couple years older. You might also look for programs like the Young Authors program, or programs through local writer's organizations near you aimed at youth.
In the fall, you might look at NaNoWriMo -- they have a youth novel writing project in addition to their annual adult program. I'm not sure about kids, but the adults have a community forum where they can share their progress and talk about what they're writing.
