I don't think she defected as such. After September 11 the WTA gave players the oppotunity to play under different countries if it was possible for them to do so and seeing as Kim is married to a Swiss guy she decided to play under the Swiss Flag in the tournaments that where going on at that stage. She is still listed on the official WTA doubles rankings as representing the US so I think that is was only a temporary thing. She said during the Swisscom Challenge last year that since Sept 11 she felt safer playing in Europe under the Swiss flag rather then the American.
What? The WTA gave the American players the option of playing under another flag!? Okay, so let's say that a top player like Jennifer Capriati wanted to play under the Italian flag because her father is Italian. Would Osama then suddenly be fooled into believing that Jen was really an Italian disguised as an American all this time?