Buying TV shows off iTunes is dead simple. Movies aren't really worth it right now; they aren't DVD quality, but it's easy enough to rip DVDs to put on your iPod if going on a trip and want something to watch (Google it, there's lots of options... I use a Mac, so don't know the windows ones).
As with music, transferring TV shows to an iPod is easy... simple actually. It's all handled by iTunes. Also, since she has such a long commute, she'd probably like to listen to podcasts, which iTunes will automatically download new shows for you, and transfer them to your iPod when you plug it in. I subscribe to a couple of NPR podcasts and technology shows, and it beats traditional radio handsdown - no commercials and a much much larger selection.
As far as a nano or full-sized iPod goes. Does she work out? If she does, the nano is much smaller and better suited for that. If she's just going to be using this in the car, then a full-sized iPod is probably the way to go. More storage and the ability to play video (as far as I know, nano's don't play video, but I would double check that at Apple's site).
Oh and lastly, you'll need a way to hook it up the car's sound system. If you have a tape deck, get a $10 tape adapter. If not, then look at reviews of the FM broadcasters, you can get one that plugs into the car's cigarette lighter, which is good for people who forget to charge things. I've heard lots of negative things about the FM broadcasters though, so go an alternative route if possible.
