An excerpt from

Helen Keller: A Life by Dorothy Herrmann

Kate Keller continued to resist the idea of putting Helen away, even though she was getting harder to handle with each day.

The Kellers by then had a second child, a girl named Mildred, who was five years younger than her sister.

A jealous Helen overturned the cradle. The baby might have died if Kate had not caught her before she fell on the floor. A short time later, Helen locked her mother in the pantry for several hours and cut off the black corkscrews of the child of the family cook who had been instructed to keep her entertained. Once Helen’s wet apron caught flame as she held it in front of the fire, and a nurse quickly threw a blanket over her, putting out the fire.

RE:
when was Helen Keller's sister Mildred born?
how much older is Helen?

But they had a site that gives Helen’s biographical information you may want to check [yay]:

http://www.greatwomen.org/wo

The Nat’l Women’s Hall of Fame… cool, huh.

perhaps she is turning 1? so maybe 1888 she was born??

edit:

nope that can’t be right cause in another letter written in 1887 she writes of her sister being sick and getting medicine and kissing her(Helen’s) teacher)

Mildred Campbell Keller Birth: 26 October 1886 in Tuscumbia, Colbert, Alabama, U.S.A. Death: December 1969 in Montgomery, Alabama, U.S.A. I hope this helps! Charles