Snowboards for women are built differently than men's boards because on average, women are shorter, have smaller feet and shorter legs. This gives a women a disadvantage if she was to use a guys board. Women snowboards have different stances, adjusted sidecuts and sofetr flex than men's boards.
And did you know your snowboard length is determined by your weight and riding style. You take in height when you are between sizes. Many snowboard manufactures put their length chart on the bottom of the board to make getting the correct length easier. So believe the manufacture when selecting your length. Keep in mind, getting a board too long is harder to handle. But getting a board too short, then you loose edging and control. So make sure to get the correct length.