Why does Becky hide under the tablecloth while Mr. Barrow talks with Miss Minchin?

From the text:

"Go back to your work, Becky," Miss Amelia had said; but she had stopped to pick up reverently first a muff and then a coat, and while she stood looking at them adoringly, she heard Miss Minchin upon the threshold, and, being smitten with terror at the thought of being accused of taking liberties, she rashly darted under the table, which hid her by its tablecloth.