Reportedly, the parents were unaware of her little arsenal. She had sold a gun she owned some years ago and the parents thought she had none. Now, you might think they should have been searching their home and her room, and you might be right, but they did not, and therefore did not know about her guns.
She reportedly was on the autism spectrum and was also “under a doctor’s care” for “an emotional disorder”. Yes, she was still living with her parents. Many young adults with autism do, as they can’t make it on their own out there in the adult world, or it takes them much longer to manage that.
The point of sharing that info is that many parents have an adult child at home who is incapable of living independently.