Future and Past can change places

One of the premises of my novel is that time is only a perception. One of my characters can leave the present at will. She runs into a potential problem, however, when she intends to show visit her 12th birthday party (a few months into the future) to see if she gets a new bike but lands instead at her 2nd birthday party, the only big kid there! How did she mix up the traveling words and how will she get out of the backyard party unnoticed?