To the ancient Greeks, she was supremely heavenly (4)
I believe the answer is:
hera
'supremely heavenly' is the definition.
I can't judge whether this definition defines the answer.
'to the ancient greeks she' is the wordplay.
I cannot quite understand how this works, but
'she' could be 'her' (I've seen this in other clues) and 'her' is present in the answer.
A single letter 'a' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'was' acts as a link.
Can you help me to learn more?
(Other definitions for hera that I've seen before include "female Greek deity" , "Divine consort" , "Greek queen of Olympian gods" , "marriage goddess" , "Regularly-deceived wife" .)