Heather time-traveling to the 1950s is the equivalent of a child right now time-traveling to the 1980s, and that is... difficult to process.
This story requires more suspension of disbelief than many other Magic Attic books, since Heather is involved in a multi-day trip and competition after traveling through the attic. The book moves along quickly, without any attention to her situation as a child traveling without her parents or a change of clothes, but it's a perfectly fine read for the target audience.