My sister accuses me of being the "favorite" all the time, although we both agree that our older system definitely was, although he passed away when I was 8.
I'm also on the autism spectrum, and my son is PDD-NOS. This Especially make connecting with others difficult, and even when people insist they do care, it's like I'm wearing a giant emotional rain coat, it just literally bounces off.
Keep trying with her though, find out what makes her tick and what makes her feel wanted and loved.
Also, there is NO such thing as too much hugging. You literally can not hug your sons enough. They need that affirmation and acceptance. Just last night I was lying on the couch at my mother in laws and my 12 year old son (PDD-NOS fellow) literally came can laid on the cough right against me like a little boy of 5 or 6 would. My wife always comments that she thinks he's too old for that, but I know better. I still want to be able to be close like that. Probably that hurt little boy in side me, but hey, I still feel it none the less.
It hurt though, because so far, nobody, family or otherwise, has ever wanted me at all.