Disclaimer: I'm not a parent of teenagers, so may well be talking rubbish.
Some of the most effective parenting responses my mother ever gave to some of my more "interesting" experiments/ideas as a teenager and young adult was by not responding at all. I can still remember her complete non-reaction, beyond a mild compliment about my lipstick, to my attempt at full goth makeup one evening. Other than that, crickets. Stopped that stone cold in its tracks with hardly looking up from her book. 😑
Consciously or unconsciously we're often looking for a reaction from our parents and for the opportunity to angrily rail against them, if given even the hint of pushback. She's obviously looking for an 'evil terf' mum to complain about, as it is part of the standard online narrative of the trans movement and she wants to feel fully part of her tribe, so that requires a bogeyman. Don't provide it for her. Her dad has the right idea, don't provide any reaction. Be boring.
You can say, "I agree with the SC ruling, but if you don't, that's fine. We’re adults and can disagree." She likely won’t accept that, but you don’t need to engage further. Set your boundaries and move on with your day.
Young adults often seek attention through parental reactions, they're really like overgrown toddlers. Engaging only reinforces the cycle. Follow your husband’s lead—don’t react to this behavior or the trans topic at all.