At the end of the each episode, you have to eliminate the most
powerful alien in the game. You will find her in the egg chute.
This is where she is best left. First, use any gun to take care
of the eggs and facehuggers. Once the eggs are destroyed, shoot
the Queen's chute to bring her down. The battle requires a lot 
of ammunition. Use the heavy weaponry such as the pulse rifle 
and smartguns. She will eventually die and you can move on to
the next level.