Longer or shorter snowboard?

my sister is a snowboarder and i want to buy her her first board for christmas but i'm having some trouble in regards to length. she is quite tall (roughly 5'9) which means that all the 'lady' snowboards are too short for her, but she is also quite skinny (roughly 60kg) so im thinking the 'male' boards might be too heavy? or something. now i have found the perfect snowboard for her taste but the size is either 152 or 156 and im not sure which to go for.. i think she usually rides 155 but i have read somewhere that for freestyle in the snowpark a shorter board is better, but 156 is only slightly bigger whilst 152 seems quite a lot shorter? help!