Karlach in Baldur's Gate 3

Be patient and move towards the Extinct Village after you solve all the issues in the Grove (what you can). From the village, go north and jump over the ruined bridge. Go right, kill the hyenas and soon you will come across a dead end. Under the rock lies the tribute collector, next to him lies the key. The path down leads to a log across the river, behind which sits Karlach. agree to help, kill the paladins and she will become your partner.