What types of things is she interested in? Art? Music? Video? Programming? Something else entirely?
All of these things domains have relatively inexpensive tools available which would be accessible enough for her to use. (I'll admit that I am not the best resource for what those tools are).
The larger philosophical approach: show her that computers are tools that she can use to pursue her own interests and to create things. Provide support when necessary, but mostly let her figure things out on her own (and show her where to look when she wants to learn more; I learned a lot about how to use Photoshop from Photoshop tutorial sites, for example). If it's something you're pretty good with, "Hey, wanna see something cool?" works better than almost anything else.
It's okay if that's the extent to which she is interested in computers. It's also okay if she begins trying to create her own tools, as there are resources for that, too.
Finally, keep in mind that 7 year olds are constantly growing and changing, and that interests can change rapidly. It's okay if she spends 2 weeks straight working on GIMP, only to drop all of that the third week. The introduction of extrinsic motivators tends to diminish intrinsic motivation (Kohn, Pink), and she's still young enough that her sense of curiousity and adventure has hopefully not been fully squashed.
Good luck.