I suspect that the aircraft slipped off the reef-shelf-”beach” - carried so, by ocean tidal and wave forces; but the she might have landed “inland” along the edge of the lagoon.
Yes, I agree, I think they landed on the reef because people heard her radio calls later, which could of only happened if one of her engines was running. She and Noonan survived the landing but the ocean probably took her airplane out with the tide and destroyed it eventually, I think both of them died on that island unfortunately.