Keira Metz is a sorceress from Carreras and she’s one of the few NPCs in The Witcher 3 with a relatively extensive questline. Here’s how to complete her questline and obtain the ‘Friends With Benefits’ trophy.
When Yennefer tasks you to start looking for Ciri in Velen, you’ll get the main quest titled ‘Nilfgaardian Connection’. Complete this quest to track down Hendrik the spy and from there, you’ll open up two other quests for Geralt. The one you want to tackle is ‘Hunting A Witch’.
First things first: travel to the village of Midcopse to gather information about the witch. You’ll notice that the villagers are rather tight-lipped about the witch’s presence in the area so you’ll have to eavesdrop on them if you want Keira’s location. Simply look out for two gossiping ladies and stand a slight distance away from them to get the information you need. After that, you should get a quest update that allows you to follow the short trail to the witch’s hut. If for some reason you are unable to successfully eavesdrop don’t worry, after some time has passed a marker will lead you to an individual who will provide you the information you need.