"She is a very quiet girl."
Translation:Она очень тихая девочка.
No, not really. Девочка is basically "a little girl". At some point during their teens, the girls "graduate" from "девочка" to "девушка", with the latter being something like "a young lady" (without sounding like the language of an old geezer). There is no sharp boundary between the two in Russian; personally I would put it somewhere around 15 years of age, but outside of this transitional grey area these words are not interchangeable.
I've found it harder that usual to keep девушка in mind, because the music group DeVotchKa has my brain hardwired from years ago. :D