The chapter below contains a complete walkthrough for Odd Grata, including screenshots and boldfaced tips.
To obtain this quest, talk to Rost during The Point of the Spear and ask him about additional matters that may need your attention (choose: Is there something else bothering you?).
First, make your way to the top of the mountain. You'll encounter two Watchers along the way - remember that a clean shot in the eye will eliminate them instantly.
The way behind these two stone waypoints leads straight to the top of the mountain and Grata's home. Once you've completed the climb, the woman will ask you to hunt a few rabbits and find her prayer beads.
Begin by acquiring the meat. The marker leads to an area with multiple rabbits. Remember that your objective is to gather five pieces of meat, not killing five rabbits. Use Focus if you having problems locating them.
Once you've picked up the meat, visit the location where Grata left her prayer beads. Now you'll have to do some climbing. To get to the top, keep climbing to the left until you reach the area shown on the screenshot above.
Stand below the rope and jump so Aloy uses it to slide from the mountain. Pick up the beads lying in the chest on the bench  and then use the protruding tree trunk  to descend from the mountain in a matter of seconds. Make your way back to Grata to finish the mission.