The only problem with the plot
is that the couple is guilty about the wrong person.
Nyagek drowning wasn't anyone's fault. She was always supposed to board the bus and cross the ocean, regardless of Bol's interference. OTOH, Nyagek's mom's was left behind to die, because her seat on the bus was stolen from her by Bol. The mom should have been the one haunting the couple, but clearly the couple wasn't guilty about her.