Katrina is missing. She disappeared overnight, and not a single soul knows where she went. The security cameras didn't even show she left the gates, which meant she snuck off and avoided the security. No one could also contact her at all. She completely went off the radar.
Truth be told, I can't think of any reason other than her running away, and even the others believe so, especially Eris, who vehemently believes that she might have eloped with another guy. I didn't believe it, though. The latter just seems odd to me.
There is also another possibility that someone kidnapped her, but that's just not plausible given the tight security of the manor. Katrina would also not just let herself get captured. I'm sure of it. Unless she was a willing captive and I meant that whoever kidnapped her was someone she would willingly go with. So Eris' hunch kinda makes sense, but also no.