While this is cool idea, how possible would it be to extend any particular scene by that short of a time? If the video is output at a typical 24 fps, the shortest any scene could be modified would be ~42 ms. Even with a lot of newer footage being filmed at 48 fps, it's still only able to clipped at a rate of 21 ms.
Past that, I've seen a small amount of time shifting take place during a not-so-careful re-encode. At 1 ms precision, even this would be enough to throw off such a tracking system.
How tech savvy is she? I've found that many people who say they want "a tablet" really only think the iPad. If she saw the Courier video, I take it she's a little more tech savvy than that, but it's still worth asking.
She has moderate skillz. We use a several different devices at home; iMac, macbook, Windows pc, HP Touchpad (cm9), Android smartphones. I think she would be willing to put up with a few quirks from a first gen device. But, the iPad feels less risky.
