People, by nature, often have a hard time dealing with what is "different" from the norm.
And they do not have, first hand experience, in dealing with children or adults, who are 'different.'
When my daughter was in Kindergarten, she had an Autistic classmate. A boy. She befriended him and was really nice to him, and his Mom always has remembered her for that.
My son who is now in Kindergarten, has an Autistic classmate as well.
Both of these Autistic children, had Aids with them in class.
Their Teachers, ALSO, taught the class, about how to treat others etc. So the Teacher also 'educated' the other kids, about basic human decency.
In my daughter's martial arts class, there is a high functioning Asperger's student. He's a great kid. No one treats him differently. Although they know he is 'different.'
Lots of Autistic kids, have many other capabilities or talents.
The world is full of different types of people.
Some of the world's geniuses, are also 'different' and may have these tendencies, but are so high functioning, that 'eccentricities' are overlooked.
Per your family's reaction to your daughter... well, they just don't know how to deal with it. And some people by nature, just 'deny' acknowledgement of it, because, they do not know how to act appropriately, toward it.
Hence, they relegate themselves to perhaps "rude" reactions to her. In light of their own kids and 'comfort levels.'
You might just casually educate them on it.
Not in a soap-box manner (because they are family), but in a real mellow manner. So that they may perhaps, "acquire" more normalcy in how they react to your daughter. When she is in their midst.
If your family is pointedly rude to you/your child, you should not put up with it. But perhaps, speak up to them in a 'friendly way. Meaning, if you don't speak up, it will only garner more frustration for yourself/ your child. But, not everyone "knows" how to deal with an Autistic child.
My son was delayed in speech as a toddler. Even with that, people were rude to him, treating him like he was retarded. He was not and was in fact, advanced in many areas developmentally, per his age. And I spoke up to people. He is a kid, like anyone else.
I know its hard, but try not letting other's attitudes, get you down.
I know, easier said than done.