A few literary techniques are used by Austen to highlight both Mary and Anne's characters. Austen tells us that Mary is a rather unattractive character:

She had no resources for solitude; and inheriting a considerable share of the Elliot self-importance, was very prone to add to every other distress that of fancying herself neglected and ill-used.

Anne is used to the role of chief pacifier of her sister's temper. Hence, the description below. You can see how Austen is trying to highlight the necessary efforts involved in mollifying (appeasing) Mary when she is unreasonable.

A little further perseverance in patience, and forced cheerfulness on Anne's side, produced nearly a cure on Mary's.

Alliteration- This is the repetition of initial consonants, usually in stressed syllables of words. Example: perseverance in patience.

Consonance- This is the repetition of consonants in stressed syllables of words. Repetition can occur at the beginning, end, or middle of the word. Example: forced cheerfulness.

Parallelism- This is similarity of structure in clauses and phrases. Example:

A little further perseverance in patience, and forced cheerfulness on Anne's side, produced nearly a cure on Mary's.