Left, you have no clue - I need to consult the map to see if you can spot a similar crack/cave opening as Haynuus can from where you are. Certainly one exists as the top and bottom ledge join with a common outer wall.
Basically, to detect Haynuus, Ameena's hearing and smell are probably best. With a good perception roll, Ameena might hear the general yells and stuff from the left, and there's an outside chance of scenting Haynuus on the air. She'd need to be uninterrupted, and certainly away from strong sounds and smells.
So yeah, if Westian can keep the undead and wasp focused on him (and away from Ameena and her nose), and as long as Ameena stays relatively close to the edge (and doens't go too far back into the cavern wall, nor go too close to the cascade) you might be able to spot where Haynuus is.
Or, you know, if Haynuus falls off the ledge and plummets to the cavern floor, you might just spot that
