Regarding appearances, well... appearances can be deceiving. I know people who look younger than they should and definitely some who look older than they are. The person who helped free Claire didn't have a tag that said, "I am XX years old." So in my opinion, she shouldn't be ruled out just because she doesn't look sixteen.

And maybe she does know who her mother is? If Walt can have special powers, why can't Alex? Furthermore, I was told that a mother-child bond is quite special and possibly strong. Maybe she saw Rousseau (sp) from a distance and felt something? As again, nothing is for certain in this show. Maybe this Alex thing is just there to think. For all we know, the real Alex may well be long dead.