Why do you think Pearl is so upset to find that Hester has removed the scarlet letter from her dress?

Pearl is upset becuase the A is what she grew up to know her mother by. She grew up knowing her mother dressed modestly, with her hair pinned back, and the letter on her chest. However the minute Hester unpins her hair, and throws the "A" away, it makes Pearl highly uncomfortably and agitated. She, like all small children are slaves to familiarity. Hester is not her true mother without the A.