Did she realize how ridiculous these very youthful, foolish manners are, she would blush for herself.

She will--when she has attained the age of discretion.
Another of our girls' mistakes is that of imagining that brusqueness and pertness are wit.

There is no other error more common with girls from fifteen to eighteen; they generally choose a boy as the butt of their sarcastic remarks--and, to their shame be it said, they frequently select a lad who is too courteous to retort in kind.
But these faults in boy and girl alike are evidences of a "freshness" which wears off as the years roll on, as the green husk, when touched by the frost, falls away, leaving exposed the glossy brown shell enclosing the ripe, sweet kernel of the nut.
If this answer to your letter reads like a sermon, pardon one who is interested in young people, and who, well remembering when she was young herself, would fain hold out a helping hand to those who are stumbling on in the path she trod in years gone by..