Girl crossing the French islands gets extremely cold (7)
I believe the answer is:
glacial
'extremely cold' is the definition.
(I've seen this before)
'girl crossing the french islands' is the wordplay.
I cannot really see how this works, but
'girl' could be 'g' and 'g' is found in the answer.
'islands' could be 'ci' (Channel Islands) and 'ci' is present in the answer.
'the french' could be 'la' ('the' in French) and 'la' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'gets' acts as a link.
(Other definitions for glacial that I've seen before include "Frigid" , "Icy; distant" , "Of slow moving ice masses" , "Relating to ice" , "Freezing - unfriendly" .)