I think, in all other respects, they're basically nymphs.
Dryads are tree nymphs. Nymphs are "minor female nature deities typically associated with a particular location or landform" (
wikipedia).
Btw, if I want to include something into a game that hasn't had much spotlight in the novels, I just hit wikipedia and steal what I can find.
I guess I would play nymphs like lesser shide, humanoid faeries with some floral/watery attributes. Probably "sponsored magic" that's associated with the location she is attached to. As they are associated with a lot of growing stuff, I'd give them a recovery power as well, and if you have a tree nymph she can maybe use toughness as well. Cold Iron as the usual faerie catch should suffice.
If you look at the wikipedia page, there are tons of different types of nymphs, depending on where they live and what they do. They are described pretty well, so there should be tons of stuff for you to build them.