Why did Beverly kenney kill herself?

i don't think it was because of her career, rock n roll or some guy. she was in pain for i'm guessing here.. some mental illness, (the record seems to say that) there is evidence that her parents were a source of pain, i don't get the feeling she had any close friends, she was an intelligent woman so she must've really wanted to die. i read in another post that her mother destroyed a letter beverly wrote to her possibly the night she killed herself bearing her soul... whatever that meant to beverly and her mother.