"It seems to me the utmost folly for a woman at the head of a household, and the mother of children, to spend in an atelier days which would be better employed contriving for the comfort of her family."

 an artist's or designer's studio or workroom

ate·lier

noun

Seriocomic

He never assumed this seriocomic tone when alone with Mrs. Pontellier.

 mixing the serious with the comic with comic predominating

se·rio·com·ic

abjective 

Bah!" and she
went shuffling and sidling on down the gallery toward her room.

move sideways

si·dle

Verb

She had possession of the rocker, and she was busily engaged in sewing
upon a diminutive pair of night-drawers.

very small

di·min·u·tive

abjective 

There was a soft effulgence in the east.

 radiant splendor

ef·ful·gence

adjective