Sarah's problem with Harry (6)
I believe the answer is:
harass
'harry' is the definition.
(synonyms)
'sarah's problem' is the wordplay.
'problem' indicates anagramming the letters.
'sarahs' anagrammed gives 'HARASS'.
'with' is the link.
(Other definitions for harass that I've seen before include "Constantly torment" , "Repeatedly torment" , "Trouble and annoy continually" , "Constantly intimidate" , "Vex - pester" .)