Since you're starting out, and based on your weight/height, I'd say you should look in the range of 141-146. Shorter will be easier to maneuver and initiate turns. My girl is just an inch taller than you and similar weight, and I put her on a 145.
I'd suggest looking into Gnu, Roxy, Never Summer, Arbor, and Bataleon. They all have some great women's specific boards with cool graphics too.
16 NS West . 15 NS Snowtrooper BIA . 13 Salomon Pow Snake
15 Now Drive . 14 Burton Genesis
14 Flow Hylite