She sounds amazing however i've not arranged anything but all my experience from what i've heard and read tells me that it's a fucking nightmare to arrange anything like this
I've attended a couple of Gangbangs and I am actually thinking it's about time I did another as the last one was about 6 years ago, that particular one was with a parlour girl who was very well known and reviewed, they also had free advertising as every bloke coming into the parlour was informed about it.
There were 10 of us who turned up but the number wasn't limited so could have been more however only 10 still showed on the day despite an awful lot of interest.
This appears to be one of the main stumbling blocks in no shows, guys will say they are 100% a week or few days before, they may still say the night before or even on the morning and then just like WG's seem to have so much bad luck and emergencies guys will suddenly be struck down with a mystery illness or the car won't start; got called into work etc etc
8 ends up being 3, 6 ends up being 2 and 4 ends up being just you

The other one I did was with another well reviewed and popular AW girl who advertised it on her AW page, she picked guys she'd seen before a few times and knew would get on with each other, from memory there should have been 5 of us but only 3 turned up and these were 5 reliable guys, apparently the other 2 did have genuine excuses but still hey
Part of the problem is how you advertise and spread the word as the site rules don't allow socials to be arranged, I believe from a recent thread this also extends to group sex sessions which is a shame and seems strange but that's the rules, you are also not allowed to request PM's so can't arrange things that way either
Personally I don't do SA / SB or any of those type of sites, not sure if she could advertise it on there or whether it falls foul of their rules as it probably crosses the blurred line between "An arrangement" and Prostitution which for US hosted sites will be a no no.
The only other way would be for her to set up an AW page and advertise it on there
Whatever you do you will need to tread carefully to avoid breaking any of the rules on here