Are any of your other fish showing any ill symptoms? My first thought was tuberculosis, because of the bend and it looks like her eyes are bulging. I found this definition so please take a quick look and see if this matches what you may have going on.
If a fish has a bent or curved spine, it is most likely infected with a Gram-positive mycobacteria (Mycobacterium marinum or M. fortuitum). This is commonly referred to as fish tuberculosis, piscine tuberculosis, acid-fast disease or granuloma disease. Tuberculosis is a chronic, progressive disease that may take years to fully develop. Symptoms include lethargy, emaciation, fin and scale loss, exophthalmia (bulging eyes), skin inflammation and ulceration, edema (dropsy), peritonitis (parasite infestation) and nodules in muscles that may cause deformation of the fish. Fish that appear to be most susceptible to fish tuberculosis are gouramis, black mollies, neons, and other tetras, carp and anabantids.
Infected fish should be removed and quarantined immediately for four weeks or more. To prevent this infection, do not overcrowd, and provide good water quality. Remove any fish that appear affected. Some successful treatments have been described using chloramine-B or -T, cyclosporine, doxycycline, ethambutol, ethionamide, isoniazid, kanamycin, minocycline, penicillin, rifampin, streptomycin, sulfonamides and tetracycline. In addition, you might try using streptomycin for the first four days at a dose of 10.6 mg/L (40 mg/gallon). After the streptomycin treatment is completed, feed the affected fish with food that has been treated (soaked in) with rifampin at a rate of 10 milligrams per 100 grams of food for about two months. At the same time, treat the aquarium with isoniazid twice a week at a 10.6 mg/L (40 mg/gallon) dosage for one month. If all fish become infected and eventually die, the entire aquarium should be sterilized using a mild bleach solution and rinsed with liberal amounts of water before adding any new fish.
Good luck, I love rainbows so I hope you have a good outcome here.
another one might be ill too now. Hint of an eye bulge and lump on the tail
