Your tank is very overstocked, sounds like it's new, and that makes me suspect ammonia/nitrite toxicity. When water conditions are poor, fish seldom become aggressive--it's all they can do to survive, much less pick on tankmates.
I wasn't quick enough to save her! It's all my fault! I crowded the tank! STUPID ME!:argh I can't believe I killed Lilly! How could I be so careless!??!