Need opinions kind of long

Ok so my niece is 4 years old. She belongs to my husband's sister. For 3 years of her life she was left in a high chair or play pen. When she was a baby they left her in a play pen in front of the tv. Didn't hardly change her diaper until it was leaking. Once she started walking they put her in a high chair. She's still not potty trained. She can't talk very well. She's supposed to start school in a few weeks. ( me and my husband taught her to walk) and when we came around we always change her diaper and stuff because it's not right for her to sit in a dirty diaper for who knows how long. Were not always around so we can't do everything she needs. I know it's her parents job but they suck as parents. Anyways...recently they took her to the doctor and the Dr said she has adhd and autism. I believe she does have adhd but I've also been studying up on autism and I think they misdiagnosed her. I think it's just neglect. I think if she was properly cared for that she would be fine. Oh and the annoying part...they are trying to draw a check on her. Niether of her parents work. They just depend on handouts. So anyways my question is do you think it's just neglect or could it really be autism. I mean she's hyper but she's behind because of her parents not caring