Chapter 6 of The Scarlet Letter is devoted to the subject of Pearl in its entirety, and there are numerous quotes describing her actions and appearance. These are just a few of those quotes;
"Pearl's aspect was imbued with a spell of infinite variety; in this one child there were many children, comprehending the full scope between the wild-flower prettiness of a peasant baby, and the pomp, in little, of an infant princess."
Pearl's appearance and essence were hard to define; there were many contradicting aspects of her presence. On the one hand, she showed the simple beauty of a "peasant baby," while on the other hand, she had an aura of royalty about her, like a princess.
"Her nature appeared to possess depth, too, as well as variety; but - or else Hester's fears deceived her - it lacked reference and adaptation to the world into which she was born."
Pearl, from a very young age, showed a very complicated nature; her mother thought, but was not sure, that she seemed unconnected to the world, and did not easily conform to its rules and requirements.
"The child could not be made amenable to rules. In giving her existence, a great law had been broken, and the result was a being whose elements were perhaps beautiful and brilliant, but all in disorder."
Pearl could not be made to obey. This attribute of hers was seen as a disorder; having been born as a result of the sin of her parents, it stood to reason that her nature and appearance, though "beautiful and brilliant," would be askew as a consequence.
"Pearl would frown, and clench her little fist, and harden her small features into a stern, unsympathizing look of discontent. Not seldom, she would laugh anew, and louder than before, like a thing incapable and unintelligent of human sorrow. Or...she would be convulsed with a rage of grief, and sob out her love for her mother in broken words, and seem intent on proving that she had a heart, by breaking it."
Pearl was completely unpredictable in her actions, and in her responses to her mother's moods. She might react with discontent, or inexplicable laughter, or rage, or tenderness to any given stimulus; there was no rhyme or reason to her actions (Chapter 6).