My DD1 who is on the spectrum didn't start flapping until she was 4 1/2! She did do finger flicking though but that only started around 13-14 months.

I think if you are aware of the "signposts" for ASD, you may pick some up and get concerned, if by 2 she hasn't reached some milestones, or has issues with speech it maybe a good idea to get her checked out by a behavioural paediatrician or a speech therapist jic. Up until then, just keep an eye on her and trust your instincts!