Opportune Parry and Riposte is not an attempt to 'hit' anything. They include that it is an
attack roll as if she were making an attack of opportunity
but then goes on to state
If her result is greater than the attacking creature’s result, the creature’s attack automatically misses.
It is an attack like an attack of opportunity for the purpose of abilities (feats, spells, etc) that affect those things but your only goal is to roll greater than the target (the rare exception to 'meets beats'), not hit anything. Your GM may wish to allow an automatic success, but there is nothing in the rules that specifies that it works.