Answer:
She meant a royal and wealthy class.
Step-by-step explanation:
Materials made of purple and fine-linen were especially difficult to sew and were thus reserved for the royal families in ancient times. When Pauline was thinking about Joan she acknowledged that even though Joan's father did not make much as a countryside doctor, Joan dressed well enough and had an air that belonged to the purple-and-fine-linen class. This means that Joan had the disposition of a wealthy child.
Pauline could think of Joan in this light because she was a wealthy snob.