The organiser is right - how can she tell? She is not in a position to know the genitalia of the people attending, unless she demands you all strip naked?
With rare exceptions, it’s obvious on sight, fully clothed, even from a distance.
But this thread is a perfect demonstration of how much it messes up so many of our societal conventions when men who claim they are women insist they are women and must be able to access all women’s spaces and events.
The organiser can no longer tell, when people apply to attend, whether they are male or female. Even asking for a picture of their passport or other document is not reliable.
So if she does choose, out of consideration for her female clients, to segregate sleeping accommodation by sex, it means that she will have to meet all new clients before she can allocate rooms. If some rooms are shared, she will have to make sure there’s some flexibility built in. Unless she waits until all guests have arrived, she won’t be sure how to allocate. And knowing how touchy some clients might be about having their sex referred to, however obliquely, she will likely not want to make it obvious by shifting people around, once the allocation is done.
She can choose not to do this, of course, but I think she would lose clients rapidly and word would go round.
The other alternative, which is to make it clear on booking that single sex exemptions are being applied, puts her at risk from transactivists who often target single sex spaces, even in such obviously reasonable organisations such as rape crisis and DV shelters.
The end result, of course, is that many organisers will stop organising such trips altogether. Others will continue, but shared accommodation, unless organised by those booking in as a group, will not be feasible and everyone will have the increased expense of single rooms.
And all this, because rather than accepting that they are male, but want to present as female, men are now demonstrating their power to enter wherever they like and overrule all the societal norms that have been developed to protect women.
Incredible that a genuinely disadvantaged minority, like lesbian women, are having so much taken from them, with the backing of governments, society and the law.