Dammit. I'm too tired to make this all nice and sweet. So, sorry for this, but I'll jsut link you my delicious-bookmarks for s1 and s2 (all gen). I'm basically a Dean-slightly-more-favoring-girl, so your friend should be fine with them.
Sadly, I don't have them listed by length, so there're a few that aren't long.

Oh, and for LONG, she should start reading "In Reverse (http://www.fanfiction.net/s/2787883/1/In_Reverse): After Faith, a job has the boys looking for missing hikers in Wyoming. While Sam worries it’s connected to what happened to Dean ten years ago, Dean wonders if Sam would be better off back in the world of normal.

Ok. Here are the bookmarks:
For season one-fics (http://www.delicious.com/Marlowe97/gen+s1?page=1)
for season two-fics (http://www.delicious.com/Marlowe97/gen+s2) (definitely read "Rush", which is the first on that list!)