It has been proven in the past that women are more careful drivers than men and can therefore be seen as less of a risk. Various companies have now been setup to provide insurance for lady drivers only. These companies tend to offer a slightly cheaper premium as because they offer only to a low risk category; you are not paying extra in your premium to cover the cost of people who are high risk.
For an insurance company offering insurance to Lady drivers it makes sense, and they are easily able to reduce their premiums if they are not as likely to make as many payouts.
However, women will only really benefit from this type of policy if they have an insurance history and have built up their no claims discount. You may also find that even if you are a woman, if you are too young, or have previously made claims, they may not offer you a policy.