She's a month at the eye centre (4)
I believe the answer is:
mary
'she's' is the definition.
'a month at the eye centre' is the wordplay.
'a month' becomes 'mar' (short for March).
'at' says to put letters next to each other.
'centre' says to take the centre.
The middle of 'eye' is 'y'.
'mar'+'y'='MARY'
(Other definitions for mary that I've seen before include "Successor to Edward VI" , "See 2" , "could be Wesley" , "-- Queen of Scots" , "feature of 21/23 [NATIVITY SCENE]" .)