If you were AE/FN in 1937 on NIKU, would you have moved the dead body of your companion far away from the beach, the plane and Seven site? I don't think so. They were thirsty, hungry, exhausted and maybe hurt. They would have erected the grave near the plane or near the place they choose for waiting.
Ever move a dead body? Not easy under the best of circumstances.
The available evidence suggests that the bones found by Gallagher were female. He also found parts of a woman's shoe and parts of a man's shoe which suggests that, at some point, there were a man and a woman cast away on the island. The woman, or at least the bones found by Gallagher, were not buried, so ...
- either Fred died first so there was no one to bury Amelia
or
- Amelia died first and Fred, for whatever reason, didn't bury her.
It's natural to make the assumption that whoever died first would be in some way buried by the survivor but it's dangerous to make any assumptions when we're dealing with a situation we can only begin to imagine. The easiest place to dig a hole on Niku is out on the beach in the sand. Digging a hole inland in coral rubble is hard, hot work even if you have a good shovel (been there, done that), but dragging a body from the Seven Site out to the beach might also be beyond the ability of a debilitated castaway, male or female. Piling coral rubble on the body might be the only option but we see no sign of anything like that at or near the Seven Site.