Yep, she plays a Peter Jackson made up Elf, Tauriel. Although given the way the movies may break up into 3 parts, I suspect there is a chance that she might not show up until Part 2 and Part 3. Of course, PJ managed to work Arwen into the Two Towers movie even though she never appeared in that book so I don't presume to be correct that Tauriel would be limited to only the later chapters.
I watched LOTR again about a month ago, and found it more difficult to enjoy this time around, as I had read the books not long before. Glorfindel getting bumped at the river for more Arwen time cheeses me off.