This is a missable Trophy in itself, and by not doing this will also cause you to miss out on Full Crew - Bring all possible allies to Kaer Morhen for the battle against the Hunt. (Secret)
To set things in motion, you need to complete the Main Quest "Hunting a Witch", this introduces you to Keira.
Another Main Quest opens thereafter, "Wandering in the Dark". Upon completion, talking to Keira will give you the option for Secondary Quest "Magic Lamp".
To unlock this Trophy, agree to help/find/goto/fetch/assist in everything!
After "Magic Lamp", you will be offered "An Invitation from Keira Metz" - this consists of 3 smaller quests (A Towerful of Mice, A Favor for a Friend and For the Advancement of Learning).
If you have agreed to all her demands, you can talk to her and suggest another way to keep her safe - propose to send her to Kaer Morhen,
Keira's sub-plot is then marked as complete, your Trophy will unlock and progress toward Full Crew is also made.