Read this sentence from paragraph 11. The invitation alone was nicer than anything she owned.
The author includes this sentence most likely to demonstrate that —
Diane lives above her means
Diane is a selfish and greedy person
Diane feels insecure about her social status
Diane wishes she could afford expensive invitations

Diane feels insecure about her social status

Explanation:

Diane thought that the invitation to the event was nicer than anything she owned at that point. This is very unlikely as it is just an invitation so the reason it seemed nicer to Diane than her possessions was because she was insecure about her social status such that anything from people she considered higher in status than her, looked better than whatever she could possibly have.

d.) then bernice winced as marjorie tossed her own hair over her shoulders and began to twist it slowly into two long blond braids until in her cream-colored negligée she looked like a delicate painting of some saxon princess. fascinated, bernice watched the braids grow. heavy and luxurious they were, moving under the supple fingers like restive snakes—and to bernice remained this relic and the curling iron and a to-morrow full of eyes.

i think descriptive but i'm not 100% sure.. sorry.