Fate - hers is occasionally entangled with mine (7)
I believe the answer is:
nemesis
'fate' is the definition.
(nemesis can mean someone's doom or fate)
'hers is occasionally entangled with mine' is the wordplay.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
'entangled with' indicates an anagram.
'hers'+'is'='hersis'
The alternate letters of 'hersis' are 'ess'.
'ess' anagrammed with 'mine' can make 'NEMESIS'.
(Other definitions for nemesis that I've seen before include "Goddess of revenge - seems in (anag)" , "Greek goddess - opponent who cannot be beaten" , "Avenging deity" , "curse" , "Siemens (anag.)" .)