Harriet Nicholson, 60, was pronounced dead Sunday morning at Bellevue Hospital.
Nicholson had been in critical condition since the tragedy on October 4.
Her daughter, Sonia Marra, 40, was also killed in the crash.
Marra's partner, Helen Tamaki, 43, died a week later.
Nicholson's husband and the pilot survived relatively unharmed.
The chopper was beginning a sightseeing tour when it plunged into the water right after take-off.