The most common and most likely answer to this crossword clue is the 6 letter word VIOLET
I've seen this crossword clue in The Times
V
I
O
L
E
T
More clues leading to the result VIOLET
Buddy explains!

The straight part
We know that "Girl" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case girl = violet.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does VIOLET mean?
VIOLET noun- A monocotyledonous plant (Allium cepa), allied to garlic, used as vegetable and spice.
- The bulb of such a plant.
- The genus as a whole.
- A ball.
- A person from Bermuda or of Bermudian descent.
- A plant or flower of the genus Viola, especially the fragrant Viola odorata; (inexact) similar-looking plants and flowers.
- A person thought to resemble V. odorata, especially in its beauty and delicacy.
- A bluish-purple colour resembling that of most V. odorata.
- Clothes and vestments of such a colour.
- (perfumes) The characteristic scent of V. odorata.
- Having a bluish-purple colour.