Sideways fish

Question
I bought 2 female crowntail betta fish at Petco.

One is white with purple fins, the other is green with black fins.

The green one stays sideways constantly. She eats, she takes breaths, but she mostly floats sideways in the tank.

I kept her in her own tank for 4 days after I bought her, expecting her to die any minute. But she kept going. Eating, pooping, breathing, swimming sideways.

So I went ahead and added her to the main tank with the rest of the fish, and not much has changed.

What's wrong with her?

Answer
Desirai,

There could be a couple reasons. What are your water perimeters and what is your heater set at. It should be between 80 and 82 degrees at all times. Swim bladder disease could be another problem. Try fasting her for 2 days and on the third day feed her a cooked shelled pea and then fast again for 2 days. Make sure she is able to get to the top for air. Weekly water changes are very important. Keep an eye on the other fish. They might start picking on her. After trying the pea, let me know how she is doing.