In the middle of flat strip, she washes (9)
I believe the answer is:
laundress
'she washes' is the definition.
(I've seen this before)
'in the middle of flat strip' is the wordplay.
'in the middle of' says to take the centre (I've seen 'in the middle' mean this).
'strip' becomes 'undress' (synonyms).
The centre of 'flat' is 'la'.
'la'+'undress'='LAUNDRESS'
(Other definitions for laundress that I've seen before include "A professional lady washer of clothes" , "Disguise for jailbreaker in famous tale" , "She'll clean" , "Washerwoman" , "Cleaner" .)