Is it OK to have girl-referees?

Wow.  Not really sure where to start.  Super Rugby (and the NRL) have fitness standards for referees and touch judges.  Men and women have the same standards and are evaluated after the game using the same criteria.  Either they're good enough or they're not, and to get promoted means they've worked years of lower grade games.  I guess when a male referee calls Six Again during the Grand Final and then decides right after that he didn't, or misses an obvious forward pass that anyone with eyes should have seen it that it's just human error, or makes a horrible mistake during the decider of State of Origin then it's just "oops" but if a female official made these mistakes that it would be because of their gender.

If it's distracting to you, you'll adjust.  Or find something else to watch. 

Yes, that is okay. It's happening more now in sports.