What reveals the calm lady on the summit is a princess? (3,6,8)

'a princess?' is the definition.
Both the answer and definition are singular nouns.
Perhaps you can see an association between them that I can't see?

'what reveals the calm lady on the summit' is the wordplay.
I cannot quite understand how this works, but
'what' could be 'eh' (sound used to ask 'what?' or 'pardon?') and 'eh' is found within the answer.
'lady' could be 'her' (her refers to a woman) and 'her' is found within the answer.
'on' could be 're' ('on' can be mean 'with reference to') and 're' is present in the answer.
This may be the basis of the clue (or it may be nonsense).

'is' acts as a link.

Can you help me to learn more?