Well, it depends a lot on your budget also. If you are not worried about graphics, You can buy a basic one woth about 2 GB ram and 100gb Harddisk. I use my laptop for same purpose as your sis is going to.. I like Dell laptops, I love their after sales service. However, i myself has a Toshiba
a little cheaper, but just as good for someone who isn't going to use all the bells and whistles, and doesn't need all the horsepower behind it.
I might even suggest the Dell Vostro... Nice price and 3 year warranty to go with it and she can have XP Pro put on it... she can upgrade as she wants or leave it and still have a decent notebook. Keeping it as is, but upgrading the NIC and the 3 year accident coverage is 1k... worth it to me, since I have the XPS M1710 and take it every where...