First Lady not heartless in meeting (5)
I believe the answer is:
'meeting' is the definition.
(meeting is a type of event)
'first lady not heartless' is the wordplay.
'first' is a charade indicator (letters next to each other).
'lady' becomes 'eve' (I've seen this before).
'heartless' means to remove the middle letters.
'not' with its centre removed is 'nt'.
'eve'+'nt' is 'EVENT'.
'in' acts as a link.
(Other definitions for event that I've seen before include "A notable occurrence or happening" , "riding competition" , "special occasion" , "case" , "celebration?" .)