BobWards.com: 5150 Ladies Dynasty Snowboard (05) - A step above the rest for women wanting to charge (Ladies Dynasty Snowboard (05)) Info
I got that for my girlfriend for Christmas. I did a lot of research on snowboards and this was the only womens board from 5150 that I found worth it. Check on Ebay, I paid 133 CAD shipped brand new in the plastic.
Basically, look for a board with sidewall construction, sintered or sintruded base, at least triaxial fiber glass weave and a wood core. Those are the important specs to look at IMO.
You don't want cap construction and extruded bases are slow and don't hold wax at all.
My girlfriend got the 149 and she is 5'4" 117lbs, if you are just starting, I'd get ~145 cm.