[Mary]'s mother [Amy] had given her a gift certificate so [Mary] took her sister [Natalia] out to eat.
('Natalia', 'Amy')
[Mary]'s mother [Amy] had given her a gift certificate so [Mary] took her sister [Natalia] out to eat.
[{('Natalia', 'mother', 'Amy'): [('Natalia', 'sister', 'Mary'), ('Mary', 'mother', 'Amy')]}]
['sister', 'mother']