.. How do I defeat the Countess?

This is going to take some cooperative work between the team members here. I hope you saved your game, because this may take a couple of tries.

As Lauren, talk to the Countess through all options until she attacks. What do you have in inventory that might make a good weapon?

Grab the lighted cigarette in your inventory and use it on the Countess.

You now switch to Joey, who gives you a hint by telling the Countess he needs to be saved, thus turning her attention on him.

What you want to do here is lure her out onto the balcony as far as she'll go. To do this, talk to the Countess so she takes a step toward you, then take a TINY step left and talk to her again.

Repeat this process. If you move too far left, she'll lose interest and turn back to Lauren, and you have to start again. Grind your teeth and do so.

Keep going left until Joey is hanging in midair beyond the balcony and the Countess is standing on the balcony as far left as she'll go. If you've gone far enough, your POV will suddenly shift back to Lauren.

Now, as Lauren, go out onto the balcony and ... well, left-click on the Countess. Bye bye!