A female also up in the air (5)
I believe the answer is:
afoot
'in the air' is the definition.
(I've seen this before)
'a female also up' is the wordplay.
'female' becomes 'f' (abbreviation).
'also' becomes 'too' (synonyms).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'too' backwards is 'oot'.
'a'+'f'+'oot'='AFOOT'
(Other definitions for afoot that I've seen before include "Making progress" , "Progressing, in operation - like Sherlock Holmes's game" , "In the pipeline" , "in the air" , "in preparation" .)