Females are very, very timid. And therefore they stress very easily. I have a male that has done quite well for several months now (sourced via DD).
I started with a pair, but that female had a swim bladder issue from the start. Acquired another female from DD a few weeks later, and she struggled to adjust for a several weeks before she secluded into permanent hiding.
I've spoken with the person who landed a female trio from DD, and he reported similar difficulties getting all three adjusted and acclimated to a closed system. Although he did eventually succeed in getting all three eating and mostly adjusted.
It seems females are tough to handle; males are much hardier.
Best of luck.