The Measure of Modesty from the Written Torah

To the questioner, 

The commandments of the Torah were given as general directives, and from them we understand the will of Hashem. 

Verse 1 - And there shall not be seen among you any unseemly thing, and He will turn away from you - Deuteronomy, chapter 23, verse 15.

Thus Hashem is among us, but when there is revealed nakedness, He, as it were, removes the Divine Presence from among us, Heaven forbid. 

Verse 2 - When you go out as a camp against your enemies, and you shall guard yourself from every evil thing - Deuteronomy, chapter 23, verse 10. And our Sages explained this verse clearly (Babylonian Talmud, Avodah Zarah 20b): And you shall guard yourself from every evil thing - that a person should not have improper thoughts by day and come to impurity at night. Thus, a man is forbidden to do anything that will bring him to improper thoughts during the day, which then naturally leads him to impurity at night, Heaven forbid. 

And in the Mishnah in tractate Zavim (chapter 2, mishnah 2), our Sages said that even if a man merely sees a place on a woman that is not modest, even if he has not yet thought about it, that alone can bring him to impurity at night. 

It turns out that a woman who walks immodestly in a place where a man can see her is directly causing those men who see or think about the matter during the day to come to impurity at night. It follows that she is the one who caused them this sin, nullifying the fulfillment of the verse And you shall guard yourself from every evil thing for them, and therefore she is responsible for all the men who came to impurity because of her lack of modesty, and she is punished for this. 

Verse 3 - And Hashem said: Because the daughters of Zion are haughty, and walk with outstretched necks and winking eyes, walking and mincing along, and making a tinkling with their feet [a terrible punishment will come upon them, as explained later in the verses]. The prophet Isaiah, chapter 3, verse 15. 

The explanation of the Malbim: Outstretched necks [and winking eyes] - standing upright and looking with the eyes. Walking and mincing, like a small child running. And making a tinkling with their feet - making a sound. That is, the girls did all these things because of their lack of modesty, and so that the men would look at them and think about them, and they caused the men to be deprived of the command And you shall guard yourself from every evil thing; therefore they were the ones severely punished for this.

May it be Hashem's will that your friend’s heart be moved to want to accept upon herself to dress and conduct herself with proper modesty when standing in a place where there are men who can see her; and in that merit, may it be Hashem's will that she merit a husband who will truly appreciate her and especially value all of her virtues. 

With blessing,

Rabbi Nachum