When it comes to parents who have kids with mental issues, parents are often in denial. I've witnessed it.I still don’t understand your anger towards the parents. You were successful, because you were trying very hard and eventually it worked. Why do you think that they weren’t. The little factual knowledge I‘ve seen is that they found a gun and made her sell it.
A few years ago, at a shooting range, I was chatting with a father whose daughter had Autism. The father was watching me shoot & during a break, he said, "Hey, you're pretty good; I'd like some advice. My daughter is 10. What kind of gun would you recommend for her? She's autistic, so I was thinking something simple like a revolver."
I said, "Well, maybe a different hobby would be better for her."
He got angry & said "Oh, man," & walked away.
Parents of kids with mental issues often try to erase the stigma of mental illness & prove their kid is "normal" by encouraging them to do things that are inappropriate for them, then bragging about it. Like Adam Lanza's mother - who bought guns & ammunition for him.