Bikes and kit for women
Women have shorter arms, a shorter trunk, narrower shoulders, smaller feet and hands and proportionately longer legs compared to men. Oh, and different pelvic bone structure too. This means that women's bike frames generally need a shorter top tube and stem. Now that sloping top tubes are accepted in both road and off road designs, there are many more bikes which really fit women.
Saddles are a particular issue
Many manufacturers are now making cycle clothing for women, too: tops are a bit shorter with narrower shoulders, appropriate length sleeves and perhaps a broader hem. Even stretchy lycra cycling shorts need a broader cut hip, narrower waist and higher rise to the waist, but most importantly the position of the padding needs to be different from men's shorts.
It's worth checking out some components for best fit too. Women usually have small hands so brake levers, handlebars and grips need to be such that they can apply the brakes without difficulty.
Saddles are a particular issue. Women's saddles tend to be wider and shorter than men's saddles to cater for women's broader pelvic bones. A modern trend has been for the saddles to feature a cut away section in the nose so that there is no problem with pressure on the genital area. These saddles look a bit strange, but they're proving very popular!