Grey, perhaps, she's a mother again (4)
I believe the answer is:
mare
'grey perhaps she's a' is the definition.
I can't judge whether this definition defines the answer.
'mother again' is the wordplay.
'mother' becomes 'ma' (Ma is another word for mother or mum).
'again' becomes 're' (prefix meaning 'again').
'ma'+'re'='MARE'
Can you help me to learn more?
(Other definitions for mare that I've seen before include "Nag" , "Horse; lunar sea" , "Female equine animal" , "Female quadruped" , "For classicists, sea" .)