Identity is a self determined phenomena based on subjective personal beliefs & values. In other words, you don't get decide for someone else who they are.
Nobody gets to decide who they are, people have personalities and characters, which are formed by nature and nurture, we don't have 'identities'.
GI is a political construct, it has no validity, it's pie in the sky delusion, it is not some sort of universal truth, it's just something else humans have made up. A fad and fancy, which will soon pass, leaving a lot of broken people in its wake.
Sex is immutable, someone born female/male will be a girl/boy during adolescence and a women/man during adulthood. It's a material reality that can't be changed by wishing on a star, or a cocktail of drugs, or mutilating surgery, and no amount of bullshit will change that.
My sympathy to the mother, it must be her worst nightmare, it must be akin to your child dying.