Mavis lost time with her fooling around (8)
I believe the answer is:
throstle
'mavis' is the definition.
('throstle' can be a synonym of 'mavis')
'lost time with her fooling around' is the wordplay.
'time' becomes 't'.
'with' is a charade indicator (letters next to each other).
'fooling around' indicates anagramming the letters.
'lost'+'t'+'her'='lostther'
'lostther' anagrammed gives 'THROSTLE'.
(Other definitions for throstle that I've seen before include "Young thrush" , "Song thrush -- short let (anag)" , "birdie" , "Bird - short let (anag)" , "Mavis" .)