Hmmm...I would start by going as simply as possible. I apologize if this is too dumbed-down. Depending on my students, I start out really slow and basic and speed up as I know they're getting it. So please don't be insulted if I broke it down too much!

How familiar are you with the voice-over commands? This video provides a good, basic demo: https://www.youtube.com/watch?v=RMJGeJd2PiQ

1. Begin by having Voice Over turned on already. As she becomes more adept at using it, she can learn to turn it on or off herself. If she is used to using synthesized voice, leave it on the default speech settings. If not, slow down the voice.
2. Show her the button to get to the home page. Explain that the home page has all of the apps on the device. They form a grid pattern on the screen. Let her know how many rows and columns there are. She can basically move through them like a list. When she flicks her finger to the right, the device reads the next item on the list. Each time she flicks, it goes to the next one. When she hears the one she would like, double tap the screen to open it. If she would like to move backward in the list, flick to the left.
3. To understand the concept of "flicking" to the right and left, begin with hand-under-hand. You make the gesture with her feeling you do it. When she understands what you mean, have her do it. You could also do hand-over-hand where you guide her fingers. Do this so she understands the double-tap too.
4. Model for her how to open an app so she can hear what exactly the voice-over commands sound like when navigating the menus and opening an app.
5. After she has these basics, let her play around and explore the device. That's the way we learn best, right? When she's ready for more, and you're ready:

What I feel are more advanced commands for navigating with Voice Over:
https://www.apple.com/accessibility/itunes/ipodtouch.html

If you need ideas for apps, let me know.

Please let me know if that helps!