I joined an "all girls" guild on another game and their verification process was simply to ask if you identified as a girl. Not in voice chat, just a written question wherever you happened to contact them (forums, Discord, in game, etc). That was it.

Were there men in the group pretending to be women? Maybe. The moderators understood though that making sure no one was harassed or taken advantage of was more important. As long as you followed the rules no one worried about who might have lied to get invited in. That group was truly free from judgement because no one was told their voice was too deep, that they didn't look feminine enough in a photo, or that they used improper pronouns. We were all queens.

From what I've seen on this thread sounds like this group could learn a thing or two from them.