Here Kristy was just trying to help and her brother had to be a jerk. Sure, maybe he had every right to be short with her, but Kristy didn't think that it was quite fair considering her self-appointed position as relationship-fixer.
"Yes, I did," she stalled. "I, uh, haven't been able to get a hold of Mary Anne and she was supposed to tell me how Stacey...was doing."
She managed not to end the sentence as a question, but just barely. Kristy started cursing herself for lying because now she was either going to have to stick to it or admit that she was making things up.