Because it is not the place of anyone to tell anyone else that her lived experience isn't real - just as, for example, it was not the place of Piers Morgan to tell Meghan Markle he didn't believe she'd been suicidal. You can't ask people to let who they are be subject to debater, and no one can know a person better than that person knows herself.

You're essentially saying she should have to justify HERSELF to you. Since someone like you would simply never accept that a person like the author knows what she has lived, how can it be anything but arrogance and psychological abuse for you to set yourself as the person to whom she must prove her own validity?