She's over anger about start of affair (5)
I believe the answer is:
erica
'she's' is the definition.
'anger about start of affair' is the wordplay.
'anger' becomes 'ire' (ire is intense rage).
'about' says the letters should be written in reverse.
'start of affair' becomes 'ca' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ire' reversed gives 'eri'.
'eri'+'ca'='ERICA'
'over' acts as a link.
Can you help me to learn more?
(Other definitions for erica that I've seen before include "Female" , "Heath genus; girl's name" , "Heather, for instance" , "I care about Heather, oddly" , "Girl's name - I care (anag)" .)