I agree with trailfleet its sounds like she is upset about something has she siblings does she go to day care , can you think of anything in her life would be upsetting ?
Autism? Probably not.
However, you might wish to google the phrase "bipolar in toddlers" to see if the behaviours described on the internet remind you of your granddaughter. Mental health issues can be genetic (the opposite is also true); however, I do know that the earlier the diagnosis, the better the prognosis. I say this not to scare you but to make you aware that early treatment and intervention can often "stave off" the more difficult attributes of certain mental health issues and disorders. Hoping I'm wrong ...
I don't believe this is a sign of autism. She is only 2 years old and she is not sure how to her frustrations. I feel that with someone working with her and showing her other ways to handle this stress she will be fine.