Her ado brought a mild exclamation of concern (2,4)
I believe the answer is:
oh dear
'concern' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'her ado brought a mild exclamation' is the wordplay.
'her ado' can be anagrammed to 'OH DEAR'.
Though, I am not clear how the anagram is indicated.
'of' is the link.
Can you help me to learn more?
(Other definitions for oh dear that I've seen before include "Never mind!" , "What a pity/shame/surprise!" , "alas" , "That's a shame" , "I say" .)