Why does Olivia think she is an awful person?

Olivia thinks she's an awful person because she doesn't want her parents to come to the show..... because she doesn't want Auggie at the show.

Then why are you crying?
Because i'm an awful person.
What are you talking about?
She's not looking at me, wiping her tears with the palm of her hand.
Ihaven't told my parents about the show, she says quickly.
Ishake my head because i don't quite get what she's telling me. That's okay, i say. it's not too late, there are still tickets available—
Idon't want them to come to the show, Justin, she interrupts impatiently. Don't you see what i'm saying? I don't want them to come! If they come, they'll bring Auggie with them, and i just don't feel like . . .