I got this reaction from my step daughter when I first met her. It drove me nuts! Still to this day I sometimes get the "ignore" or the " look the other way " . Once I relaxed and stopped forcing the relationship she came to me.

I think some kids just need time to figure someone out.

I would continue to do what you're doing and let mom know what's going on and see if she behaves like this at home.

If you do something really fun, like play cars with the other kids, will she approach you to play?

I agree with you... drives me crazy when a child doesn't answer me! LOL They're kids, they do it. But it is one of my big pet peeves!