A few new tidbits of info from this article:
https://ktla.com/news/california/search-intensifies-for-missing-southern-california-girl-15/
"The trip [from dad's house to aunt's house] should have taken about 20 minutes. However, around 8 p.m., Allison’s aunt called her father to say she hadn’t arrived."
This answers the question about whether the aunt was expecting Alison to come over. It seems she was. Alison left her dad's house at 6:20 p.m. and the aunt called at 8 p.m. to say she hadn't arrived.
“If she ran away, which I don’t think she would – she’s not like that, just come home,” pleaded Annie Chao, Allison’s mother. “It’s going to be okay. I just want to make sure that you’re safe. I just want to find her.”
Mom doesn't think Alison would have run away.
h