Despite what she'd said about family structure among the batponies -- that they were so disconnected to the point that what an Equestrian would think of as a 'family' didn't seem to exist in their culture at all -- her brother must really mean something to her. That was the best explanation Artemis could come up with for Purity’s behaviour, outside of the even stranger suggestion that somepony from a school of mercenary assassins didn't like killing -- which would certainly be inconvenient, given her profession! 