3x3, about 10" min. above. She'll be massive. You're gonna need more veg time though.
I'm gonna predict that as big as she is now, your net will eventually be just supporting buds.
If it's a true SCRoG, let her start going vertical now, hit the screen & stay open. Don't wanna give advice that might mess up the fluxing, but she is setup perfectly to go vertical for the screen. Anymore horizontal training & SCRoG would be unnecessary. The screen's job is to do what you already have, which is horizontal training. It's almost either/or at this point in my opinion. Too long of veg & she'll turn to wood on you.
Either way, the screen will help, even if just for branch support.
Hope this makes sense.