About to run race? She'll tell you all about it! (9)
I believe the answer is:
raconteur
'she'll tell you all about it' is the definition.
(a raconteur is a storyteller)
'about to run race?' is the wordplay.
'about' is an anagram indicator.
'to'+'run'+'race'='torunrace'
'torunrace' with letters rearranged gives 'RACONTEUR'.
(Other definitions for raconteur that I've seen before include "Teller of anecdote" , "source of anecdotes" , "He's good at telling stories" , "After-dinner speaker, maybe" , "one with a gift for relation" .)