She was watching naruto fight a powerful akatsuki member called Pein and decided to go into "hero" mode and "save" him. After Naruto repeatedly told her to stay away and get out of there, she proclaimed her love for him and charged at Pein. She, of course, didn't even get close before Pein smashed her to the ground, creating a large crater, and if THAT wasnt enough to do her in, he also went up to her and stabbed her in the stomach. Naruto and Pein, of course, continued fighting after her death
Wooow, it's no certain that she's dead though...
She did die but after Naruto talked with pain he revived all those killed during the recent pain invasion of konoha
Hinata never died, sakura healed her BEFORE nagato revived everyone