Show clearly how niece gets upset about five (6)
I believe the answer is:
evince
'show clearly' is the definition.
(I've seen this before)
'niece gets upset about five' is the wordplay.
'gets upset' is an anagram indicator (I've seen 'getting upset' mean this).
'about' indicates putting letters inside.
'five' becomes 'V' (Roman numeral).
'niece' is an anagram of 'eince'.
'eince' enclosing 'v' is 'EVINCE'.
'how' acts as a link.
(Other definitions for evince that I've seen before include "Manifest, show" , "Show or display, say feeling" , "Make clear, show (quality)" , "Show or reveal, say interest" , "Indicate (something)" .)