I bought Morrowind GOTY for my husband six years ago, intending not to play it. I watched him play for several hours and then decided that yeah, I was going to give it a go. Now he doesn't have a hope of getting on SKYRIM until January 2012 at the earliest.
Basically...just have her watch you play for a while. Do interesting quests and really show off the world. If she's as big a fantasy fan as you suggest, she'll get hooked.

(Also, to the "show her the clothes and shoes she can buy" response above? Yeah, that's not going to work. There's a serious lack of GOOD clothes and shoes.

)