Who is Ada in Alice in Wonderland?

Ada is a girl who Alice knows who lives in the real world. While Alice is trapped in the hall of doors, she wonders if she has been exchanged for somebody else. Ada is one of the girls who she speculates that she may have become.

But if I'm not the same, the next question is, Who in the world am I? Ah, THAT'S the great puzzle!' And she began thinking over all the children she knew that were of the same age as herself, to see if she could have been changed for any of them.

I'm sure I'm not Ada,' she said, for her hair goes in such long ringlets, and mine doesn't go in ringlets at all; and I'm sure I can't be Mabel, for I know all sorts of things, and she, oh! she knows such a very little!