In my experience the first step to good mental health is being honest with myself.
If Simone Biles is being honest with us (and I've got no reason to believe that she's not being honest,) she says she felt she couldn't perform at the right level - borne out by her earlier performances - and that she didn't want to drag her team down. Would she have been doing the right thing for the team if she went out and flubbed it? I would argue not. Let's not forget that there were three other ladies who did stand up and took Silver.
She now has to deal with this, and get herself right for the rest of the events. She's the Greatest Ever and yet she was dragging the team down? Come on, man. That must suck. I can absolutely see how that might bring someone into a vicious circle of beating themselves up, and for her to be able to be honest with herself is laudable. Maybe it will be easier for her to get her head right, without feeling like she's letting down the team if she doesn't succeed. I can easily believe that might be the case without her "just being out for herself," or whatever.