There was a brief glimpse of her in action in the showreel they screened at Comic Con. There was so much cool stuff in that showreel, I’m completely jealous of everyone who got to see it! I’m DYING to see these movies! Is it December yet? How about now? NOW?!
My guess is she’ll be in both movies, part 1 when the Dwarves and Bilbo are captured in Mirkwood, and part 2 at the Battle of Five Armies. Anyway, here’s what was said about her from Comic Con:
Tauriel, barely shown in these clips, although Philippa speaks highly of her in the Q&A which follows. What we do see is a female, dressed in-brown version of Legolas, in combat with goblins. Legolas springs out of… leaves? …and joins in the fighting.
Whole showreel summary is here: http://www.theonering.net/torwp/2012/07/14/59080-the-hobbitcon-hall-h-presentation-torn-round-up-part-one/#more-59080
This is from the Q&A part of the panel:
Q: “What kind of role does Galadriel play, and are there are any female characters you added?”
Philippa Boyens: we did feel the weight of it being a “boys’ own” story. After a while, you’d feel the weight of it. And we did create a character. Her name’s Tauriel, who is an elf. Who is played magnificently by Evangeline Lilly. Who you saw a little bit of. She’s our redhead. We created her for that reason. To bring that energy into the film, that feminine energy. We believe it’s completely within the spirit of Tolkien. You know, we tried really hard, and she wanted that more than anything, herself. She didn’t want it to be a ploy. We wanted her to sit in the world, and I think you guys are going to fall in love with her.
Transcript of the whole Q&A is here: http://www.theonering.net/torwp/2012/07/16/59194-full-transcript-of-the-hall-h-hobbitcon-qa/#more-59194