Hilda is upset about a bloomer (6)
I believe the answer is:
dahlia
'bloomer' is the definition.
(I know that dahlia is a type of bloomer)
'hilda is upset about a' is the wordplay.
'is upset' is an anagram indicator (I've seen 'are upset' mean this).
'about' is an insertion indicator.
'hilda' anagrammed gives 'dhlia'.
'dhlia' placed around 'a' is 'DAHLIA'.
(Other definitions for dahlia that I've seen before include "Large-headed flower" , "Flower genus" , "Showy garden flower" , "Ali had (anag) - showy flower" , "Plant of the daisy family" .)