The most common and most likely answer to this crossword clue is the 9 letter word BEDIZENED
I've seen this crossword clue in Independent
B
E
D
I
Z
E
N
E
D
Buddy explains!

The straight part
We know that "gaudily dressed" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case gaudily dressed = bedizened.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 BEDIZENED mean?
BEDIZENED verb- To ornament something in showy, tasteless, or gaudy finery.
- To dirty; cover with dirt.