While Gavin holds Rosa at gunpoint, send Joey down to Lisa's consulting room to discover --
-- that Gavin really did kill Lisa, who was so traumatized by it that she's blocked the entire incident from her mind and reverted to phony psychic mode. Nothing Joey can say alters that, and we don't have time to let her gradually figure it out on her own.
If talking won't do it, we need to show her something instead. Remember what she was looking at the last time we were here?
Go into the living room to find the photo of her grandfather and blow on it twice to waft it into the consulting room.
Talk to her about the photo, and eventually even she can't avoid the truth. But that's not too helpful right now.
Go back into the living to discover Rosa, by herself.