What are the symptoms of a 2 year old girl suffering Autism?

[mum4bub]

Okay so my niece was born in 2014, and was normal until about the middle of 2015. She hasn't started talking yet, screams when she is taken away from something she is doing, she likes to lie on the floor of places and has also been lining her toys and blocks up, which I have heard as a symptom. She also rocks when she is about to go to sleep.
The mother had possibly been using drugs while pregnant and she was also on antidepression medication while pregnant.

I am incredibly worried about the child and I want some advice for the mum and the grandma as they are so lost on what is going on.

She had apparently been talking before her 18 month vaccination as she got incredibly sick with fevers, and rashes afterwards.

Please Help