a lot of people have their own theories on who she is.
Some say sister other say clone and some even say its her mother who has been dead fog some time now.
it can't be a clone for one reason, that reason is because we were told that she "is not a second Samus of any kind "
I do not believe that Nintendo would give samus a sister because it would change who she is.
now i think someone at Nintendo just has a thing for blonds (I mean just look at Peach, Zelda and of course Samus)
I think she is Damara, even know she had black hair but still in the comic samus had purple hair.