Strange clear bubble

[FlaNatural]

I have a young female (3 months old) who has developed a clear bubble on her gill that is about the size of her eyeball. The bubble deflates completely when she breathes in and reinflates when she breathes out. She has had the bubble for a week now, and it has not changed her eating habits, although her swimming is affected by the buoyancy of the bubble. She was in a female betta community tank (they are still babies) of which I am very diligent about maintaining water conditions. I have separated her out now though.
Does anyone know how to help her? If not, do you think she should be put down even though she still seems healthy, active, and healthy?

[dramaqueen]

I don't know what the bubble could be, but I wouldn't put her down unless she is in pain or suffering. Good luck with her.