Legally, a woman-only screening is discrimination based on sex or gender. But I'm not sure a civil rights agency should waste its resources on the issue.
Legally, Women's Nights at bars are also discrimination based on sex or gender, but most people see it as a publicity and money-making ploy (woman gets in free, the man accompanying her pays to get in and probably drinks more than she), and except for a grumpy few, no one complains about it.
I see this on a par with the Hooters hullabaloo of a few years ago, where a man sued to become a Hooters server, and most people wondered "why would you want to?"
BTW, the "Wonder Woman" movie is great! Yes it's a super-hero movie, lots of bad guys come to their well-deserved end, and Wonder Woman deflects bullets from five machines guns simultaneously.
But, it tells a great background story, and makes Diana "Wonder Woman" Prince a fully fleshed-out person.
And, it ends on an ambiguous note about human nature and good and evil. Kudos for doing so.