Three Rs regularly bypassed that girl (3)
I believe the answer is:
her
'girl' is the definition.
'three rs regularly bypassed' is the wordplay.
'regularly bypassed' means one should take alternating letters.
'three'+'rs'='threers'
The alternate letters of 'threers' are 'HER'.
'that' is the link.
(Other definitions for her that I've seen before include "In the Midlands she" , "Pronoun used of ship" , "The woman's" , "She, objectively" , "The female's" .)