Okay, losing control of the buoyancy can be caused by a number of reasons:
1. BAD WATER QUALITY
. The most common one and happens when people keep goldfish in too small, overcrowded or underfiltered systems. If your oranda is in a tank smaller than 20-25 gallons/80-100 liters, and/or you're not changing the water and cleaning the gravel once a week
, this is most likely the reason she's sick.
2. BAD DIET. If you're not feeding her vegetables and live foods along with the flakes and pellets, she may have an issue with her digestive tract. Usually it helps if you avoid feeding her for a day or two and then give her only peas for a few days until she improves
A dose of Epsom salts will also help, but be sure you change out 50% of the water and vacuum the gravel thoroughly before dosing! You can dose Epsom salt by adding 1/4 teaspoon per gallon of water. Dissolve the salt in a bucket with tank water and then add it.
3. Water pressure. If the fish is kept in a tank that's rather deep and tall than long and wide, the goldfish may not be able to handle the pressure on the body and may need the water level be lowered by a few inches.