At the end of "The Search," Odo asks the Female Changeling to allow himself, Kira, Sisko, and the rest to leave the Great Link planet. The Female Changeling permits this, stating that no changeling has ever harmed another.
How could she possibly know this? One hundred Changelings had been sent out many years (centuries?) earlier, and there was certainly the possibility that some of them had encountered each other, gotten into some sort of disagreement, and fought.
Perhaps the Female Changeling was only speaking of Changelings which she had knowledge of---those in the Link.