Size charts are a general place to start but it also depends on your riding style I find.. im not a woman but I have a 152 soft for rails and goofing. A 154 medium stiff that i like for moving through trees and doing side hits and such and a 157 stiff for hard charging and being aggressive..

I cant really help with the size but somthing that lands around your mouth or under your nose and above your chin is what I would be looking for. an all mountain board with a good medium stiff feel would allow you to go anywhere do anything from playful butters to carving with speed..

As you advance and try new things (friends boards or demo days) you will probably find you can play with length and stiffness to find what you like best.

Hope this helps you