Bride's outfit in her partner's changing area? (8,4)
I believe the answer is:
dressing room
'area?' is the definition.
(dressing room is a kind of area)
'bride's outfit in her partner's changing' is the wordplay.
I cannot quite see how this works, but
'outfit' could be 'dress' (I've seen this in other clues) and 'dress' is located in the answer.
'in' is present in the answer.
'partner' could be 'groom' (groom is a kind of partner) and 'groom' is found within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for dressing room that I've seen before include "Where actors change" , "Place to change or store clothes" , "Changing cubicle" , "Feature of a posh address" .)