The most common and most likely answer to this crossword clue is the 9 letter word GOOD-TIME
I've seen this crossword clue in Financial Times
G
O
O
D
-
T
I
M
E
Buddy explains!
The straight part
We know that "Such a girl" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case such a girl = good-time.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 GOOD-TIME mean?
GOOD-TIME adjective- (used only before the noun qualified) Who enjoys pleasurable activities without regard to the consequences.