That ample knitters site is one of the best in terms of having links to all of the places that have plus-size patterns.
I'm plus-size and if I just wanted a very basic cardigan or sweather, I'd probably use one of the patterns from the Lion Brand web site.
If you want to make her something really special, you might want to wait for that Big Girl Knits book... seriously. The patterns are just... awesome! And very flattering.
Doesn't Just One More Row
has lots of plus-size patterns, I think most all of her stuff comes in plus sizes.
You must be a great friend to make a sweater for your friend!