On alt.politics,election there is a subject line something like "world funniest joke" It is very very long and the jokes old and silly. If there's someome who sends you stupid jokes too often, follow my lead and "Edit, Copy, Paste" it on an email, with the subject line something like, "I see that your joke finally made international news," It should be ten minutes before she finally realizes that she's been conned.
OK, it's childish, but after 65+ years of crap from my sister, it's worth it!
Karl