Fascinating question. Thanks for asking it.
There were a number of problems associated with the leg from New Guinea to Howland Island.
First. Howland Island was tiny. Just over a mile long and only about a quarter mile wide. No matter how good a navigator Earhart was that kind of accuracy required almost perfect conditions, which didn't exist.
She had been very ill with dysentery in New Guinea and there's no doubt that weakened her. Her back-up plan to have a US Coast Guard vessel guide her to Howland came unstuck when she and the ship's crew became confused about radio schedule times. (She was using GMT, they were using US naval times.)
The final message received from Earhart said that she was running out of fuel and there can be little doubt that they came down somewhere in the vicinity of Howland.
In their contingency planning, they had hoped the aircraft would float long enough to allow them to unpack their life raft. It may have worked out like that but, if so, the life raft was never found.
There's a pretty good article about it here: Earhart's Final Flight.
