I was about to say, I never realized she was a reference!

But I dunno, I think Sim's most obscure parody/tribute for anyone, Americans or otherwise, may go to a prominent character lifted from the amazingly-brutal and totally forgotten Jules Feiffer satire, LITTLE MURDERS:

http://www.youtube.com/watch?v=imfWlHFEVLY (since I don't think we can embed videos in the comments)

But then again, at least Sim added "with apologies to Jules Feiffer and Lou Jacobi" in the character's appearance. Much more than Grandma got.