why does amanda stare at laura with a martyred look when she enters at the beginning

Laura is polishing her collection of glass animals, and Amanda returns home visibly disturbed. She has made an unsettling discovery. On the way to her D.A.R. meeting (Daughters of the American Revolution), Amanda stopped at Rubicam's Business College, where Laura has supposedly been taking lessons, to tell the teachers that Laura has a cold and to ask about Laura's progress. Amanda discovered that Laura has not been going to class everyday, but instead dropped out of the school after only a few days of attendance. The teacher remembered Laura only as the shy girl who trembled so much that she couldn't hit the keys.

Amanda, bemoaning the waste of fifty dollars for the tuition, asks Laura where she has been everyday. Laura, clearly shaken and guilt-stricken, admits that she has spent all of these days walking in the park or going to museums, keeping up the deception because she could not bear Amanda's disappointment.