I'd ask her what she's doing with your iPod, first
The Shuffle does the job. They're light & simple to use, ideal for workouts or house cleaning. They're especially good for random or sequential music listening.
It might get her out of your hair... but since you don't know what she wants, might pay to do some research.
If it's podcasts, or she wants to choose albums to listen to, the Nano is a better bet, with menus & coverflow.
Shuffle's are good for 'working through a list' that she could dump off the computer every day or two, but frankly in this mode, you'd be hard pressed to fill a 2GB and you'd never 'find' anything on the thing. Even a 1GB shuffle is plenty for most uses. I think Apple had to bring out a 2GB, just so it looked 'better'.
If she must have her whole collection on the thing... a refurbished Classic (which may be your least-support option, do it once and leave her with it).
Better still, buy yourself a 32 GB Touch or a Classic and hand your old one down to her.
My guess is that a Touch Nano will be out in Sept, so if you don't think she can deal with that, buy now.
As for colour? Either ask or check out what colours she wears. Since the 2GB, the Shuffle's colours are different to the ones shown on Apple's website. Not so pastel anymore, a little darker and more manly looking. It might be the same for Nanos, but I haven't seen many 'in the flesh' lately.