Time. It will ultimately settle in. Getting there can be a little stressful, but the pay off is coming.
I would suggest you not add salt. You know that it is bad for the cories and otos, but are just hoping that it will do something for the gourami. Ultimately, you have to think about ALL of your fish right now, not just the Pearl. If you are already resigned to bagging her up tomorrow morning and taking her back to the store, then just do a massive water change to give her some clean water to swim around in and let that do her some help. Hopefully, we can help her, while not harming the others.
Sorry I can't be of more help. You've had a tough go of it.