You must do this before talking to the Native Guide that you save him from Johannes (Ordo Luminis) hired by Alba/Clara father.
Bring Petrus & Vasco, Petrus can help to save the Native Guide.
After The Native Guide saved and back to his village (before he told you about the cave where Alba is hiding):
1. Do main quest Constantine's Fate: The Suffering of Constantine.
"Find the healer in Wenshaveye" (this will help with 'A Cure for Malichor quest: The Trial of The Waters' quest as well).
2. After triggering "The Naut's Secret: Sub Rosa" side quests, do not talk to the Native Guide.
3. Continue finishing the main quest "Constantine's Fate: The Suffering of Constantine". Must be completed, otherwise, Alba die.
4. Asks the other healer from San-Matheus (bring Petrus & Siora), Hikmet (bring Aphra & Siora), and lastly, Catasach (Native healer 'Catasach' be a greater option) bring Siora & someone else I pick Kurt.
Don't forget to ask him his seal to meet with Glendan, the leader of the council. It is required to continue the main quest. Meanwhile, continue "Sub Rosa" side quests.
5. Then talk to the Native Guide in the Wenshaveye for "Sub Rosa" side quests (bring Vasco & Petrus).
If you have done this right, when you come back to the cave, Alba would be standing there, instead of lying dead.
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