what does "prejudice is a convenient phenomenon that disappear at her wish" mean?
She used the word "tough" without the conviction it would have carried had he been a Southern boy. She only knew it with her mind; her ear couldn't distinguish between one Yankee voice and another. And somehow Mrs. Calhoun didn't expire at his appearance on the threshold. The supposedly ineradicable prejudices of Ailie's parents were a convenient phenomenon that disappeared at her wish. It was her friends who were astonished. Ailie, always a little above Tarleton, whose beaux had been very carefully the "nicest" men of the camp--Ailie and Lieutenant Schoen! I grew tired of assuring people that she was merely distracting herself--and indeed every week or so there was someone new--an ensign from Pensacola, an old friend from New Orleans--but always, in between times, there was Earl Schoen.