What if Cho is going to be the snitch? and she rats out the DA?????
That would totally kill her character. *weeps!* (It was just a thought... a possibility since the confirmed cast listing doesn't have Marietta listed... and we know how movies cut/chop books up, eliminating certain characters and merging others to tighten the storyline and make it not-as-complicated and drawn-out as the original novel...) That would definitely kill Harry's interest in her.
Of course the promo pic may not feature the DA in its entirety, and Marietta might be such a small part that she's not listed in the "main cast" (and will only be given a small credit line in the end of the movie), but still... to make betrayal HURT more, the betrayer would have to be more prominent (right?) . Unless they are cutting/skipping the entire "snitch" plot, bringing all of the DA to the fight at the ministry, and more students would be injured - possibly Cho - who then breaks up with Harry because she can't deal with the "danger" -- but then that screws up the story even more. *sigh*