With a sorority there is always going to be an element of stress. The key is that you minimise this stress as much as you can by taking appropriate steps. You don't just chuck three females into a bare tank and expect them to thrive.
A properly set-up sorority tank should only have a minimal level of stress involved for the females. There will be conflict, but it should not be sustained or overtly aggressive conflict. There may be spats every so often, but these do not escalate into full-blown war. Any time you are housing a semi-aggressive and territorial species such as splendens, stress is always going to come into play. However, if you manage your sorority correctly it should never escalate enough to cause serious issues.