12 monkeys movie ending???

I just recently watched the movie and my girlfriend and I have a sort of debate going on about the ending. At the end Bruce Willis still gets shot and killed and the man gets on the plane to spread the virus. On the plane there is the lady from the future sitting next to the terrorist and introduces herself and states that she's in insurance. My question is, does this mean she's there as insurance to stop the threat or insurance make sure the threat goes through? Is there any relevence to her being on the plane next to the terrorist? It seems like the movie suggests that we cannot change the future but then we see her there next to the terrorist for some reason. I just don't understand the reason they showed her there next to the terrorist at the end. Also, if Cole (Willis) had seen that dream all his life, why wouldn't he change his actions? It seems like he knew what would happen and how but he couldn't help himself avoid what he knew was coming. Please answer if you really know.