As her name suggests, she is presumably the paternal grandmother of Fa Mulan (the mother of Mulan's dad, Fa Zhou). She is fairly elderly, with white hair. However, she appears to be spunky and isn't afraid to speak her mind. She seems to be well versed in Chinese traditions.
According to the film directors, as the (currently) oldest living member of the Fa family, she has a connection with the ancestors.