Someone on the thread claims that she isn't claiming hair dye alters biology, merely pointing out that:
"'t*rfs' (his word not mine) cling to the argument that trans people are at odds with their own biology, but then they readily alter their own bodies to suit their needs when their biology no longer suits them."
Which is the nearest thing I've seen to a rational interpretation of her tweet, but even if that is what she's trying to say, it's a weak argument: no one gives a shit what (adult) trans people do with their own bodies, that's their business; we just don't think it makes them a woman or in may way entitled to any of the legal protections women need, any more than dyeing your hair makes you a natural blonde/ten years younger/a woman/anything other than a person with dyed hair.