On her website, Shelby writes -
 
"God specifically told me 2007 was the year. He showed me that me and my family were swimming in the swimming pool the day before the rapture. I interpret this to mean summertime"
 
I also note that Shelby lives in Florida. Having grown up in that state, I remember we used to swim almost year 'round (even here in Minnesota we could be swimming in May what with global warming and all :)). So it's entirely possible that "swimming in the swimming pool" doesn't preclude May, especially late May. I remember water skiing and picnicing on many a Memorial Day weekend. Rather than "summer", swimming could mean "not winter".
 
Come Lord Jesus!!!
 
Brad