I agree she stated that on page 220, but her book is well researched so I don't know how anyone could say she is definitely incorrect.
Then she was in error?
Here is where she probably erred. Each subdivision is 5-6 million years long. Adding all the subdivisions you get 30 to 40 million years. Probably just carelessness on her part or one of here writers fed her the error. No big deal. OTOH, if she knew what she was talking about she would have caught the error.
The chart at left shows the major subdivisions of the Cambrian Period for North America (Laurentia during the Cambrian). International ages (subdivisions) have not been established. The size of the bars does not correlate with the length of time for each age. The oldest unnamed age is 543 to 520 million years ago, while the remaining six ages are from 520 to 490 million years ago, each approximately 5-6 million years long.