At Fred's mentioning of sensitive issues, Katie's emotions change rapidly, from happiness at being with her friends to elation at finally being included in whatever was happening to nervousness at not being able to be as strong as she pretended to be, and finally back to elation, but she managed to keep a straight face through it all.
"Sensitive issues, you say?" She was trying not to sound like a kid in a candy shop but she couldn't keep just a tiny bit of the excitement out of her voice.