The extent of her anger (5)
I believe the answer is:
range
'the extent' is the definition.
(range is a kind of extent)
'of her anger' is the wordplay.
'of' says the answer is hidden in the clue.
'RANGE' is hidden within 'her anger'.
(Other definitions for range that I've seen before include "Shooting area - group of mountains" , "Where to cook" , "on which 'Dr Brewster Higley' felt at home?" , "Amplitude" , "Old song: ''Home on the . . . . .''" .)