She ain't moving too quickly (2,5)
I believe the answer is:
in haste
'too quickly' is the definition.
(I've seen this in another clue)
'she ain't moving' is the wordplay.
'moving' is an anagram indicator (letters are moved around).
'she'+'aint'='sheaint'
'sheaint' with letters rearranged gives 'IN HASTE'.
(Other definitions for in haste that I've seen before include "Hurriedly" , "Rapidly" , "''Marry . . . . . . ., repent at leisure'' (2, 5)" , "Rushing round" , "Quickly" .)