Even though Mary has been in NSW for nearly 7 years, the Wiltshire children she is governess for, only age once (by a few years), when Mary has nearly served her 7 year conviction.
Convict Polly McNamara has her hair cut off by the soldiers whilst still aboard the ship that brings the convicts to NSW. However, 7 years later, and Polly's hair is still very short. This was not the style at the time, and it should have grown well past her shoulders over this period.