It was easy to tell how hard Horatio was trying to accept what she said, just as she had to accept that no matter what she said, they had to tell her father, who also happened to be the (soon-to-be) King. They hadn't met yet and both titles made Thoth sound much more intimidating than he really was.
"It's OK," she said, smiling at him, "We'll wait for dad to get back from patrol to talk to him, until then we can relax." Truthfully she knew exactly where to find him and he probably wouldn't have minded the intrusion for this but maybe it would help Horatio to know it wasn't happening immediately.
