Update on injured female

Ok so Cleo made it through the night but I don't think she is going to make it. She started turning white from her tail all the way up her body. She is now completely pale and barely moving at all. I still have her isolated in the breeder box. But she isn't eating and is just barely hovering at the surface of the water. My guess from some of my research is that this is simple a case of too much stress on her what with the tail injury and new tank. She may also have an infection. I don't know whether to let her die naturally or to put her out of her misery. I worry that if she does have an infection she may infect the other fish in the tank. All of my other fish are very active and happy. I'd hate for anything to happen to them. I had a male die a couple of days ago so I am going to take him back to the pet store to get a replacement, and I think I might take the female too, if she doesn't make it. I am also going to buy some more females so that the 3 that I do have now aren't so pestered.