No she's an adult, she'd be around 20. The woman wearing white in the trailer looks like Alex as if she didn't die. Which makes me wonder, maybe she grew older faster for some reason, I mean, there is something wrong with her if she has thirst for blood so I guess a new virus and given what the leaker said it looks like it is her.
Here's something some people have pointed out
Is it just my impression or RE 8 is really using lots of concepts from major RE 3.5 plot? The rumors that the ending of the game is going to taste a bit bitter (possibly a hero dying, and 3.5 had at one time considered Leon to be the one to die).
Also RE 3.5 was supposed to tell the story of how Umbrella came into existence.
But i think for RE 8 they will tell how Spencer kidnap a girl (remember that strange local tale from this trailer right at the initial scene?) and this girl probably had special blood... Most likely this little girl from the tale is none other than Alex Wesker? Or possibly who was kidnapped was the girl´s mother? Looking back, the mother being kidnapped would make a lot of sense.
My theory is as follows (this is only my assumptions of how it could end up explaining Wesker Children so i don´t think this will be entirely how i put it here, but there is a small chance i end up getting some of it right, so if you don´t like theorizing don´t read further than here otherwise if you are into some speculations let´s delve into it...
there is a secret at this village, the Castle must have a very special thing to it (maybe a type of element with special properties) so some people that are born within it over the years displayed special "gifts". Perhaps with each generation the powers have diminished a bit, but still gave them a special blood that usually prevents them from getting sick and maybe gives then a bit higher intellect too.
During 1959 Someone from Spencer family happens to visit and stay in the castle a bit, has a forbidden romance with one the maids who live there (but she is kind of already a mistress to the count from that castle, and has already a child from that "village chief"). The maid gets pregnant but this time the child is from that Spencer dude, the count from the castle finds out and kills the man, Lord Spencer finds out later on (maybe a few months later the Lord is suspicious for not hearing news of what happened with this man of his family, perhaps the one that was killed was in fact, his nephew) and Ozwell gets the impression from a few rumors that this people might have strange tales of gifted individuals, so Lord spencer sends some troops to kidnap the maid in the forest when she is with her other small girl (but remember the maid is still pregnant with the child of spencer bloodline too). The maid surname was Wesker. The little girl is found by the witch (actually her grandmother) and returned to live with the count in the castle.
Spencer meets the castle maid, after a while she delivers the baby, this now is 1960 Lord Spencer raises the child as his own, he names her Alex W., he lies and tells her both their parents died in an accident.
Meanwhile Spencer secretly mantains Alex´s mom alive, he sees the blood of that family is truly special enough for his plans of using it with the progenitor virus, its later time to extract her eggs and from that he can create 12 other individuals (he already has Alex so in total they are 13) these would be his children.
Each of his children got sperm donors that are in fact people from Spencer´s cabal, his associates, but Albert Wesker is conceived with sperm from a special family that are old friends with Spencer, the french Fabron family. The children are raised as normal parts of these families from those associates. Altough this is kept a secret from the other 2 Umbrella founders, James Marcus and Edward Ashford.
Spencer cabal are members of his secret society, and eventually the babies are born so that´s circa 1967 (Albert is among them).
Alex is raised alongside another boy also from that family called Daniel Fabron. (Daniel is just a couple years younger than her)
Later Daniel Fabron is completing 17 years old starts snooping around about Alex´s (and his small brother Albert) origins, Daniel becomes suspicious because Spencer had been very strict about not letting Albert visit the Spencer family too much, and only Daniel was allowed to talk to Alex, perhaps because since the beginning Spencer planned to seed curiosity deep into Albert Wesker´s mind about all this old man wealth and secrets.
Spencer is told about this but he has already groomed Alex to become his right-hand in his plans of world conquest, she is a very bright teenager now and Spencer starts telling her about her special blood and that she is half spencer and half wesker so she has to command alongside Spencer in the new world, Spencer entrust her with files about all the Wesker children, she has to monitor all of them from a distance.
The plans start to unfold and they see that the new boy from Fabron´s family is taken to North America, from now Spencer considers him the most gifted of this other 12 children and will take him to be one of the chief Researcher in the Arklay Mountains Umbrella Compound.
in this scenario, the little girl from the RE 8 local tale and the woman seen with the white dress with her other associates (the one that looks a lot like Alex Wesker) are one and the same and she is in fact, Alex´s half-sister and - the maid´s daughter with the count.
Later on when Alex apparently dies (during Revelations 2) Daniel Fabron goes to Romania (he was snooping around trying to find Alex origins remember?) and he joins Alex half-sister and gives her the research he has so they create the Connections to stablish their own empire from what they gathered, possibly interested now in the child of Ethan Winters and Mia (i´m not sure if Albert and Fabron were already experimenting with the Mold before, its possible too that Albert Wesker submitted part of the money and equipments he got with his HCF to Fabron´s Connections mold research, and that probably happened back when Wesker was still somewhat unaware of Lord Spencer´s whole plan, since when it got to that point Albert put all his chips on the Ouroboros project and his other partner Excella.
The part about the baby and how Chris connects to this though i haven´t pieced much.
Maybe he realises that Fabron wants Mia and the baby so they can create an army of new W children or he is there because he was manipulated to provide the baby to these villains?
and that is all i have theorized so far... if you enjoyed please comment and see if you have other insights that might align with the theory or if you have another theory that´s cooler than this one.