Why was Aimee's mother late for her meeting at the World Trade Center in the novel, Nine, Ten: A September 11 Story?

On Sept. 11th, Aimee has learned from her father that her parents had no plans to divorce. She called her mother to apologize and caught her just as she was leaving her hotel for her meeting at the World Trade Center. When Aimee’s mother realized how upset Aimee was, she decided to stay in the hotel lobby and talk to her daughter instead of being on time for the meeting.