will just say she offed herself because of transphobes.

Being driven to suicide because people made fun of you is itself a mental illness. Normal people with a healthy mind endure, conform, or retaliate.

For example, if the other kids are kicking you all day and you find some joker put a "kick me" sign on your back a healthy person takes the sign off (conform). Maybe they find who did it and "kick me" back at them (retaliate), or metaphorically if the sign is a tease nickname they adopt it (endure).

A person who keeps wearing the sign, gets depressed that people keep kicking them, and eventually offs themselves is mentally ill - self-inflicted harm is the gold standard of mental illness.

What they're really saying is trannies are not mentally ill because actually they're mentally ill.