[Heidi] and her sister [Lorraine] went out to lunch with [Heidi]'s sister [Louise].
('Louise', 'Lorraine')
[Heidi] and her sister [Lorraine] went out to lunch with [Heidi]'s sister [Louise].
[{('Louise', 'sister', 'Lorraine'): [('Louise', 'sister', 'Heidi'), ('Heidi', 'sister', 'Lorraine')]}]
['sister', 'sister']