Horsewoman returning a bottle containing dodgy mixture (4,6)
I believe the answer is:
lady godiva
'horsewoman' is the definition.
'returning a bottle containing dodgy mixture' is the wordplay.
'returning' is a reversal indicator.
'bottle' becomes 'vial' (vial is a kind of bottle**).
'containing' means one lot of letters goes inside another.
'mixture' is an anagram indicator.
'a'+'vial'='avial'
'avial' back-to-front is 'laiva'.
'dodgy' with letters rearranged gives 'dygod'.
'laiva' going around 'dygod' is 'LADY GODIVA'.
(Other definitions for lady godiva that I've seen before include "romantic comedy film" , "Naked rider through Coventry" , "Tom peeped at her" , "Only Peeping Tom saw her ride!" , "Wife of Leofric, an early streaker!" .)