The most common and most likely answer to this crossword clue is the 11 letter word BALLETOMANE
I've seen this crossword clue in The Times
B
A
L
L
E
T
O
M
A
N
E
Buddy explains!
The straight part
We know that "being wild about Giselle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case being wild about giselle = balletomane.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 BALLETOMANE mean?
BALLETOMANE noun- A ballet enthusiast.