Ling Bouvier
Wikisimpsons - The Simpsons Wiki
Ling Bouvier was adopted by Selma Bouvier in China after discovering that she had reached menopause, in the episode "Goo Goo Gai Pan". She bought Ling after posing as Homer Simpson's wife in order to fool the Chinese authorities into thinking that Ling would be sent into a family, and not to a single mother.
She has only appeared in two episodes so far. First, she appeared in her adoption episode. Also, she had a brief appearance in "Kiss Kiss, Bang Bangalore" when the twins open the door to discover "hostage" MacGyver (Richard Dean Anderson) missing.