Solution to the missing third Little Sister bug of Bioshock at Neptune's Bounty

The first game of Bioshock had a bug at Neptune's Bounty map that, even patching, didn't let you to accomplish the achievement of rescue or harvest all little sisters and, therefore, have the "good" or "bad" ending of the game.

Even if this game is, right now, old I want to share this.

As the patch didn't work ever, here is a little guide of what to do in this case.

There is also a related bug or glitch that makes to appear a fourth little sister. This video doesn't show it and I never had that luck either... ;)