Having a trans ID'ed kid (I've had two because that's how contagious this dysphoria is) isn't a pass to suspend all thinking functions.
Transmen are part of the set, women. That's why they menstruate. Only women can menstruate, and they do so regardless of how they choose to present themselves socially.
It's actually doing a child no favours to collude with her about anti-reality statements. I think it deepens the dysphoria.
Be matter of fact. Your daughter can dress as she likes, wear her hair as she likes, call herself what she likes - but her sex is immutable, and she menstruates because she is female...males do not have a uterus, therefore, no males menstruate.
I agree with whomever mentioned emotional blackmail. Not that I think any feminists will fall for it, but it's not even helpful to the dysphoric child long term to fall for it. Put it this way, most children whose dysphoria persists into adulthood? You'd rather they grew up to be a Fionne, and not a reality denying numpty, right?
Anyway, it's hard to parent children and teens. Big kids, big problems, right? But the fact that it's hard - in all sorts of ways - is no reason to gaslight women.