When Terry Rockefeller heard that the World Trade Center had collapsed, she had no idea her younger sister Laura was inside. All she knew was that Laura was working in New York on Tuesday and Wednesday before coming to visit her in Boston on Thursday. As a freelance conference hostess, Laura could have been assigned to any hotel or restaurant in New York. Rockefeller had been leaving angry messages on her sister’s answering machine all day, wanting to find out where Laura was and if her travel plans would be affected. Then a little before 5 p.m., she got the call. Laura had been working at Windows on the World, on the top floor of the north tower.