Did Helen enjoy any advantages as the first child of the family?

Helen Keller actually had two older half-brothers from her father's former marriage, but she was the oldest of the children that her father, Arthur Keller, had with Kate Adams, his second wife.
Keller herself seemed to believe that being the oldest of her cohort of younger siblings gave her advantages. In her memoir, she states:

I came, I saw, I conquered, as the first baby in the family always does.

According to Keller's memoir, the next oldest sibling did not arrive until after Helen turned five. That left her with the advantage of being the only young child in the house, which allowed her to have the bulk of her mother's attention. Helen mentions having a close and loving relationship with her mother. She describes, after she became blind and deaf, being able to crawl into her mother's lap for comfort if she had had a tantrum or felt bad.
She experienced sibling rivalry when her sister Mildred was born. Luckily for her, Helen had the advantage of being the older of the two, meaning it was easier for her to terrorize the baby rather than the other way around.
It is hard to speculate as to whether her parents would have lavished such concern on her education and well-being if she had been a younger child. One hopes they would, but clearly they had extra concerns about finding a teacher who could absorb her attention and teach her to communicate after the younger children came along. The younger siblings were at risk from her uncontrolled temper and inability to articulate her needs.