Camilla Belle didn't need a fashion stylist for this look because it was pulled directly from the Gucci Spring 2011 catwalk. From head to toe, she rocks my absolute favorite runway ensemble and this season's most stellar trend--colorblocking. This is a simple ensemble to recreate, simply because it involves solid colored basics.
You can recreate the look using the pieces I selected above, or you can do your own shopping around to find the best deals. On a side note, I would check vintage shops for an orange blazer. Chances are, you'll be able to find a great, bright colored blazer for a great price. You can also adjust the color palette according to your own personal taste. If you aren't up for wearing a bright orange blazer, a beige blazer would make a great substitution. Or you can sub the bright green pants for a pair of black trousers instead.
Modify the look how you see fit, but remember that the most essential part of this ensemble is colorblocking!