Because i was looking in the trailer at 3:07 and i saw a girl.
Its not Sarah because this girl is taller.
Its not Rebecca because this girl is not pregnant.
And not Clementine because Clementine is with the girl. But that hairstyle looks like the one Becca has and she i wearing Shel's jacket
But you cant see her face so it is not comfirmed ( Just like Kenny/Nick)
And here are 2 pictures :