Been meaning to have a go at this and update my last picture of Her for a while so here we go. I mixed her appearance up a bit from her bio just coz reference pictures were impossible to come by and I like it this way. So there.
Bio of Yavanna: 'Giver of Fruits'; one of the Valier, numbered among the Aratar; the spouse of Aule; called also Kementari (thanks Silmarillion index! n.n)
...In the form of a woman she is tall, and robed in green; but at times she takes other shapes. Some there are who have seen her standing like a tree under heaven, crowned with the Sun; and from all its branches there spilled a golden dew upon the barren earth, and it grew green with corn; but the roots of the tree were in the waters of Ulmo, and the winds of Manwe spoke in its leaves. (pg 18, Of the Valar, Valaquenta, Silm.)
Pose: Alessandra Ambrosio from her website
Dress pattern: [link]