You don’t want her overtaking you! (7)
I believe the answer is:
nemesis
'overtaking you' is the definition.
The definition suggests a singular noun which matches the answer.
'you don't want her' is the wordplay.
I cannot really understand how this works, but
'her' could be 'em' and 'em' is found within the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for nemesis that I've seen before include "Fate" , "Retribution personified" , "Figure of retribution" , "Something causing misery (or death) - Meissen (anag)" , "The Greek goddess of divine retribution and vengeance" .)