Has Simon Biles specifically explained what the sources of her stress were?
What is her story about yesterday? Has it been general or specific?
I don't know--I haven't seen anything, but that doesn't mean there isn't something that she has said.
I've seen several on here talk about her sexual abuse, her adoption, her abandonment as a child, etc. Those are certainly heavy issues. They may very well be a contributing factor to what happened yesterday.
Or they might not be. Let's be careful not to explain her mental health with assumptions, etc.
Anectodote--we fostered a boy with extreme baggage--abuse of all kinds, neglect, malnourishment, etc. His story would bring you to tears. He had a very rough go as a teenager. Got in trouble with police, poor decisions, fights at school. As he is getting a little more mature and talking about some of it, he is able to dilineate when it was his demons from the past and when he was just being a teenage jackass and it was all on him. It is interesting to listen to him when he is open and honest. Sometimes we have overplayed our empathy by pointing back to his terrible early years and he'll respond that we are making him sound like a "failure" (meaning we are insinuating that because of his past, he is doomed to fail).
My point is that these things are complex. If we automatically assign all of her mistakes going forward to Larry Nassar, we could be denying her the dignity of her own decision making in life. And maybe we'll never know--this could all be personal to her to such an extent that she'll never explain it to all of us.