It seems like that's the way the spell works regardless, once the spell is cast, for 8 hours of concentration. But I'm asking if Levanna could initially cast the spell as part of a conversation without anyone knowing what has happened.
I would probably let you do it with subtle spells with a Deception roll... you could get some bonuses by maybe doing something extra to distract the subject or people around you... so long as the components are all there. If your staff is your Arcane Focus it counts as the M, and the "talking" part could be ingrained into the V part of you casting