First you need complete the Main quest Hunting a Witch
in Velen, while on you find Keira Metz. With her you complete the Main Quest Wandering in the Dark
and then ask to do the Sidequest Magic Lamp
for her. Complete it to get the Sidequest An Invitation from Keira Metz
Then there are tree Sidequests (A Towerful of Mice
, A Favor for a Friend
and Advancement of Learning
) that you need to complete. If you have a Conversion with Keira you don't to need to be nice to her but don' t use the leave Conversion option with the X, if you do that the Quest will fail!
For the last Quest Advancement of Learning
: Here you can kill her or walk away (Quit conversion Icon), you get the Achievement after.If you kill her the Full Crew Achievement will be not unlockable!