Hi Postmodern,
You should prolly give a Wood Nymph belief according to age. Since they are near ageless you can do something like for every 200 years they get 10 belief as long as they have decendants.
Its not much as Wood Nymphs do not have many offspring (like thier darker cousins). But a 1000 year old elder is possible and could take on a New God.
There will be more rules on this in another book coming soon.