From where Feferi sits, she can't exactly see very well. This is clearly the one and only fatal flaw of her plan, and nothing else. She can only see outlines where the approaching figure's shadow blocks out light between the leaves, but now she can't build herself a view port, since she'd have to practically take the whole thing down and build it again. Survival 101, Feferi, always build yourself a viewport.

This will have to do. She's hunted worse before anyway, in the depths of the oceans. It wasn't that much different. She waits until the figure gets closer, trying to figure out just how close it is, even with the lessened depth perception. When she thinks it's close enough, she jabs her makeshift spear out from the pile, aiming for the legs. Disable the target first, then she can worry about what to do with them.

Feferi Peixes, mighty huntress. All in all, she's pretty proud of herself in that moment, shoving a pointy stick through a crack in a pile of leaves and sticks and branches. She's done pretty good for herself.