Although some of these may not seem to be specifically on "modesty" they do address the root issues many girls deal with, such as fear of man, love of the world, honoring parents, and standing alone.
I Timothy 2:9-10
In like manner also, that women adorn themselves in modest apparel, with shamefacedness and sobriety; not with broided hair, or gold, or pearls, or costly array; But (which becometh women professing godliness) with good works.
I John 2:15
Love not the world,
neither the things that are in the world.
If any man love the world,
the love of the Father is not in Him.
Luke 16:15
And he said unto them, Ye are they which justify yourselves before men; but God knoweth your hearts: for that which is highly esteemed among men is abomination in the sight of God.
Proverbs 31:30
Favor is deceitful, and beauty is vain: but a woman that feareth the LORD,
she shall be praised.
Proverbs 21:2
Every way of a man is right in his own eyes:
but the LORD pondereth the hearts.
II Chronicles 16:9a
For the eyes of the LORD run to and fro throughout the whole earth, to shew himself strong in the behalf of them whose heart is perfect toward him.
I Thessalonians 4:4-6
That every one of you should know how to possess his vessel in sanctification and honour; Not in the lust of concupiscence, even as the Gentiles which know not God:
That no man go beyond and defraud his brother in any matter: because that the Lord is the avenger of all such, as we also have forewarned you and testified.
Proverbs 21:2
Every way of a man is right in his own eyes: but the LORD pondereth the hearts.
Exodus 20:12
Honour thy father and thy mother:
that thy days may be long upon the land which the LORD thy God giveth thee.
I Peter 3:3-5
Whose adorning let it not be that outward adorning of plaiting the hair,
and of wearing of gold, or of putting on of apparel;
But let it be the hidden man of the heart, in that which is not corruptible,
even the ornament of a meek and quiet spirit,
which is in the sight of God of great price.
For after this manner in the old time the holy women also,
who trusted in God, adorned themselves, being in subjections unto their own husbands:
Romans 8:5
For they that are after the flesh do mind the things of the flesh; but they that are after the Spirit the things of the Spirit.
II Corinthians 6:17
Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean thing; and I will receive you.
Romans 12:1-2
I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service. And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God.
Ephesians 6:12
For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.
I Corinthians 10:31
Whether therefore ye eat, or drink,
or whatsoever ye do,
do all to the glory of God.