How can you say that Helen as a child was sensitive and emotional?

In her memoir, Helen Keller describes herself as a sensitive and emotional child. As she gets older and her brain develops, she depicts how she becomes increasingly upset and unhappy with the limited life she is forced to live. She is also sensitive enough to know her mother loves her, and to know she owes what is "bright and good" in her life before Miss Sullivan comes to her mother's wisdom and caring.
Nevertheless, Keller remembers scenes that show how emotional she was. For example, when she realizes that other people communicate using their lips, she becomes frustrated when she cannot:

This made me so angry at times that I kicked and screamed until I was exhausted.

Helen is also jealous when her baby sister is born and tries to upset the cradle with the baby in it, showing both her desire to monopolize her mother's attention and her emotional upset at the presence of a rival.
Not long before Miss Sullivan's arrival, she writes of her outbursts, and her need for her mother's love:

If my mother happened to be near I crept into her arms, too miserable even to remember the cause of the tempest. After awhile the need of some means of communication became so urgent that these outbursts occurred daily, sometimes hourly.

Finally, her ability to respond to Miss Sullivan's love and return it shows Helen to be both sensitive and emotional. She is able to be deeply grateful for her teacher's presence in her life.