The difference which is implied through the detailed description of the Bohemian Marys and the other girls who worked in town is the following one:
The Bohemian Marys spent time having fun, unlike the other girls who continued to act seriously.
Check this fragment out: "Others, like the three Bohemian Marys, tried to make up for the years of youth they had lost." That means they tried to compensate for the time they did not spend living as young people are supposed or expected to live: enjoying life, that is, having fun. When they moved to town, all they wanted was to have a blast.
As for the other girls, it is said that, "after they came to town, (they) remained as serious and as discreet in behaviour as they had been when they ploughed and herded on their father’s farm." In other words, they continued to act seriously.
