Arelyn goes prone and slowly crawls 10’ along the cliff face towards the valley, then hides behind a bush or tree, then crouches and readies an action to attack the other person as soon as they break cover.
Spoiler
Hide: (1d20+4)[18]
Move silent if necessary: (1d20+4)[24]
Attack: (1d20+1)[10]
Sneak attack: (1d6)[6]
Damage: (1d4+1)[4]