Poor hen. She looks miserable.
First it would be helpfull have have a proper diagnosis. Other diseases such as Newcastles disease can give similar symptoms.
Most medical texts will advise seperating the patient from the rest of the group. But, by the time most keepers have even identified a problem the infection will have already passed to the rest of the group. Add to this that stress exacerbates the symptoms making it harder for the bird to recover and in most cases being seperated from the group causes high levels of stress in chickens.
You may already know, there is no cure. You may also know that many chickens survive the diseases albeit with episodes throughout their life.
Some people report alleviation of symptoms with antibiotics but antibiotics have a major downside and that is they will kill all bacteria, good and bad and this can make recovery more difficult for the bird.
Rather than washing her eyes with saline I would try thyme in warm previously boiled water. You make a thyme tea basically and strain it through very fine cloth or similar.
Unfortunately there isn't anything you can do to make sure any bird doesn't catch Mycoplasma. Once in a group of chickens it's there to stay. It transmits through the egg and through the air. Vaccination as chicks doesn't prevent a chicken from getting the disease, nor does it stop the chicken being a carrier and spreading the disease. What it can do is reduce the severity of the symptoms.
