In 1501, Catherine arrived in England and married the heir to the English throne. No, not Henry. His older brother Arthur. Yes, Henry wasn't actually suppose to be King either. A few months into their happy marriage, Arthur gets sick and dies. Catherine quickly goes from Queen-in-waiting, to widow-no-one-really-knows-what-to-do-with. Thus, Henry VII decided to do nothing. Nothing can't hurt, right?
Finally, in 1509 Henry VII croaked. Surprisingly, there was little mourning throughout the land...
The new king, Henry VIII, decided that Catherine was cute and nice, thus married her almost instantly. After several years of waiting, Catherine was finally Queen of England. No wonder she didn't want to give it up so easily...