Sansa E series (260/270/280). You can find them all day long new for under $100, or refurbished for closer to $60.
http://www.amazon.com/SanDisk-Sansa-Player-MicroSD-Expansion/dp/B000ETVKHE/ref=pd_bbs_sr_1?ie=UTF8&s=electronics&qid=1227457971&sr=8-1
Clean interface, easy to use, can be modded up with rockbox if she's so inclined, and no Apple/Microserf restrictions. However, the screen is small, so if she wants something to watch videos often, then there are better options.
If she's looking for a primarily VIDEO player, then you need to look bigger...3.5 inch screen or more. Creative Zen, Archos 6 series, Cowon D2 or A3...