She's undisturbed by a reverse (4)
I believe the answer is:
anna
'she's' is the definition.
(I've seen this before)
'undisturbed by a reverse' is the wordplay.
'undisturbed' becomes 'an' (I can't justify this - if you can you should give a lot more credence to this answer).
'by' says to put letters next to each other.
'a' becomes 'an'.
'reverse' says the letters should be written backwards.
'an' in reverse letter order is 'na'.
'an'+'na'='ANNA'
Can you help me to learn more?
(Other definitions for anna that I've seen before include "-- Wintour, editor" , "and eleven, twenty four across heroine" , "___ Pavlova, Russian dancer, d. 1931" , "- - and the King of 22" , "Book by Tolstoy" .)