The most common and most likely answer to this crossword clue is the 7 letter word PIN-UPS
I've seen this crossword clue in The Guardian
P
I
N
-
U
P
S
Buddy explains!
The straight part
We know that "pretty girls" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pretty girls = pin-ups.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 PIN-UPS mean?
PIN-UPS noun- A photograph, printed in a magazine or other publication, of a sexually attractive person (often nude or provocatively dressed), and intended to be removed and pinned up on a wall.
- The person so depicted.
- Figurehead, person who represents an idea, cause etc.