In reference to Ella and Nico (both are 'perfect spawn' in his eyes so are they both equal to him in value for his needs?)
I think "perfected spawn" just refers to level 5 superhumans. Spawn seems to be the monster name for superhumans.
The Arbiter referring to Ella as a perfected spawn suggests it wasn't after her.
I suggest that the "her" it was seeking was Aglaecwif.
The eye searches for "their chosen".
"But I must, there is more I need to do here. Someone I need to see. Their chosen."
Aglaecwif refers to Ella as "chosen"
Female "I was tasked by that cruel woman, but after what she's dragged my children and I into... I'm in no rush to follow her commands. Even if she is chosen."
Additionally, the eye is sure that Goliath knows where this chosen is
"They're consumed and devoured, their bodies, their memories, surging through each tentacle up into my body, through my spine and into my skull."
You ".......They don't know? But wait... He does."
scene elinv 803 with dissolve
"I look to the west, and see a colossal figure."
"A monstrous creature so large that its head is obscured from the clouds."
And once he consumes his memories, he goes straight to Ella.
From MC's fight with Deryl we can observe that they fight in different spots and if Goliath knew where Aglaecwif was, Eye would just go back to where MC fought Hydra Deryl, not in Ella's cave.
So I think that Aglaecwif is unlikely.
But could it be Ella? Due to her being referred to as chosen, and Eye looking for a chosen, it's likely, but we can't be sure.
The Eye says that Ella's "beautiful face" seems familiar. The "beautiful" part suggests that MC's memories and thoughts are mixed in a bit which means that it didn't recognize her from Goliath's memories.
So it's either that the method it used to get the memories was weaker than usual, since it decided to spare Goliath, or Ella is not really the target.
While it doesn't exactly fit, due to the reasons I explained, I still think that Ella is the more likely person to be the Eye's target.
A more complicated theory could be that Ella has something inside her that makes her special, perhaps some entity, and that's what the Eye is after. Perhaps that's the entity that Ella comunicates with, telling it to go back to sleep.
That entity could be the reason why monsters follow Ella. For some reason the Eye can't immediately see whatever it's looking for. Instead it only sees 2 level 5 spawn and tries to make sense of the scene.