The following option best supports the inference that tan believes nonstandard English is no less valid than standard English :
Tan winces when she describes her mothers English as broken.
Tan winces because she considers her mother’s nonstandard English as her mother tongue. It is perfectly clear and natural to her. It is full of vivid descriptions, clear observations and imagery. Nonstandard English is close to her heart because it is the language that helped her to make sense of the world.