Walking in on her, you'd think she had done something terrible wrong - it was the way she giggled and hid something behind her back. It turns out she's hiding a bowl of tuna! She was scared that you'd see it and be totally grossed out. It doesn't bother you at all.
She finds it really sexy that you aren't bothered by her tuna breath. In fact, it's especially sexy to her and she doesn't mind showing you her mouth and breathing on you.