Modesty is one of those unavoidable topics that comes up when faith and femininity come around. The past three summers, I had the treat of having a modesty/dress code talk of sorts with staff at a Christian summer camp. The difficulty with modesty is that irregardless of what you've dressed your body in, the observer is also responsible for what they perceive. A man or woman could be completely covered and could still ogled by another with lustful intentions, and that sin belongs to the ogler alone.
With that that being said, we do owe our brothers and sisters in Christ support in our shared goals of a holy life. This means dressing and behaving in a modest manner that does not create unnecessary temptation for those around us.
It can tempting to take modesty to two extremes: pushing the blame entirely on the wearer or entirely on the observer. The wearer cannot be held responsible for the decisions made by another; whatever is being worn does not justify the observer's actions. We are each responsible for our own sinfulness. However, dressing with intention to lead another to sin has its own implications for the wearer. Intending to cause another to sin is a sin.
Modesty demands a middle ground. There is no sin in making an effort to look nice or to dress yourself in a way that is empowering. Wear that dress! Style your hair! But when the dress gets tugged down to show a little more cleavage or the shorts are chosen because they are just so short... we are allowing a master manipulator lead more than just ourselves astray. We may not be our brother's keepers but we are called to love and support them!