Unheeded prophetess (9)
I believe the answer is:
cassandra
'unheeded prophetess' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for cassandra that I've seen before include "Person who prophesies disaster, after Greek legend (9)" , "was unbelievable" , "Crass Dana as gloomy prophetess" , "Jane's sister" , "Prophetess during the Trojan War whose predictions were true but never believed" .)