id say contact your local gov funded centre for treatment and development i.e.: Erin Oak Kids. they will gladly help you approach discussing with parents so they will listen. Some ideas may include Showing them brochures and explaining that help in ontario is FREE until the child is 6 yrs old and there is usually a long wait list. i know in Peel we have PEP Start Program not sure what Toronto has. i'm sure you have done all this but explain that its better to have their child assessed and find nothing wrong than to not have them tested and find out later that early intervention would have been better. Tell them how much you love their DD and want her to excel just as they do.
She may not have autism she may just be way too babied especially from being home with grandma. Plus cultural differences could be to blame too. But I fully understand the concern especially given your work history.
You're doing a good job and i would suggest doing what you can to keep her with you because if she goes somewhere else she may just fall through the cracks.
Keep it up sounds like you are the only voice she has. speak loud and clear.