She has nothing on which to subsist (5)
I believe the answer is:
olive
'she' is the definition.
(I've seen this before)
'nothing on which to subsist' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'on which' is a charade indicator (letters next to each other).
'to subsist' becomes 'live' ('live' can be a synonym of 'subsist').
'o'+'live'='OLIVE'
'has' acts as a link.
(Other definitions for olive that I've seen before include "Oil producer" , "yellowish green" , "Girl's name - colour" , "Small green Mediterranean tree-fruit (5)" , "Its branch is a peace emblem" .)