What can i do about this GIRL?!?

So me and this girl used to be good friends (i'll call her Cara) but after kindergarten i moved to a public school and she stayed in the private school that i had went to. But her family's extremely wealthy/rich and she gets whatever she wants now and is really rude to her parents (she's only 11 and calls them by their first name) and i get really embared around her because she has this huge mansion as a home and we have a small colonial styled home and her clothes are amazing! their top designer stuff sometimes but normally just ralph lauren, abercrombie, gap, or hollister. but i just found out that we're having dinner at their house on saturday and i have NO IDEA how to act or what to wear or anything. PLEASE HELP! :(