After killing the demon, Justice will be somewhat locked to your party until the confrontation between Aura and Justice at Vigil's Keep. Aura will be upset by the possession of Kristoff's body and leave. Justice will request aid in seeking out Aura at her house in the City of Amaranthine. Aura can be found in the back left room of the Chantry of our Lady Redeemer. Ensure that Justice is in the party.
In order to get a (+10) approval from Justice during this scene you need to choose either option 1 or 2 because option 3 gives (-3) approval from Justice
"I think so, yes." (+10)
"I don't think there is a right thing, here." (+10)
The encounter with Aura can be completely avoided by walking back against the left wall until you reach Vigil's Keep - Throne Room if you wish to unlock Justice from the party.