When I ran the adventure, the "one-hour" she was late took a couple of real life hours to role-play out. And to be honest, by that time, all of the PC's were SO freaked out by the other guests, and SO freaked out by the events happening, that Lashona came off as normal. They knew they were only there to make contact with her and not get themselves arrested, and it was all they were worried about.
If you really feel like cranking up the freak out factor, remove the gimped manocores that deliver the meal, and substitue in the Zombie Centars that have cooked themselves in an oven, then come out, and cut peieces off themselves to serve to the guests.
If you have a character with True seeing though, let them see. She is a silver dragon. That cat will be out of the bag at the end of the next adventure anyway. If a character starts to cast a spell (such as detect evil) while with her, go to initive, and if she wins, have her refuse to allow the casting of spells in her home. She could also attempt to disrupt it in a way that doesn't provoke an all out combat, and talk her way out of hostilities if the caster is offended, or attempts to start a fight. She knows at this point they are no real threat to her.