I couldn't really tell if it was Willa or not, but if you can tell it's her THEN IM SO HAPPY! That was the biggest hope for me (much more than the let down of Mirage Arena), as I feared she was too popular with Arrow now to come back.
And the trailer is done! Watch the uncompressed version here!
It's most distinguishable if you compare the shouts when Red Eyes crashes into Aqua and knocks her down, in both versions.