First off why is she at Lex's party?
We have all seen all the trailers ( because non-fans would not be reading this) and my take away after viewing the latest trailer.. Lex is trying to recruit her in his battle of the gladiators. Also let me just get this out the way THIS IS LEX LUTHOR! why else would he have emaculuate shiny dome?
Enough. Further evidence of her in the final battle proves that either Lex told her something or he just gave her the creeps. Plus it is a no-brainer that she knows that Superman is that dweeb Clark Kent. Obviously Bruce and Lex also knows. At that party I also believe that Clark has yet to battle the Gotham Guardian. ( if he did,he x-ray the bat and who doesn't know Bruce. I digress) If Superman was there then Doomsday would not be that big of surprise.
This is where Wonder Woman brilliance comes into play. She will be there to tell the World's Finest that Lex created this monstrosity and the Batman will speak with Lex. The bald bastard will be waiting in his Kryptonian body armor that he made from the remains of Zod's when he took flight. Superman and Wonder Woman (possibly Aquaman all that fire water?) will destroy Doomsday. Batman will show why he is the Batman and out think Lex. How does Wonder Woman find out all of this? I believe Mercy Graves might be an insider or Diana simply plays Lex. Jena Malone is also in this movie and she has to be Batgirl. Bruce would never let another Robin occur, so we will see. These all are guesses so no spoilers and please leave comments if you disagree or agree.