A plethora is too much for her (5)
I believe the answer is:
thora
'her' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'a plethora is too much' is the wordplay.
'too much' says the answer is hidden in the clue (the clue hides the answer plus unneeded letters).
'THORA' is hidden in the letters of 'plethora is'.
'for' is the link.
Can you help me to learn more?
(Other definitions for thora that I've seen before include "lady" , "Actress, dame, who died in 2003" , "Woman" , "Hat or change for a girl" .)