The big caveat is whether or not Riot is going to maintain their inter-dimensional racial heritage. As is, the current horizon points to them being made into singular beings of old times (hi Darkin), rather than interlopers. In respect to their current story ...
Kayle isn't misguided, only a product of her society. She's a living enforcer of civilized order, as her people understand and dictate the idea. The necessities of this position generally force people into a binary perspective, by far and large giving them great moral agency and clarity in what they do. When this position is challenged, they can only fight against it because it would undermine their personal integrity. It's a very classical argument from Dungeons and Dragons, specifically with regard to Lawful Good aligned beings (Paladins, etc).
Good as dictated by a society can be atrocities in any other. Honor killing is a popular gray zone for this: if society, in both culture and religion, dictate honor killing as the morally just route, a Lawful Good being following this procedure is in fact Lawful Good. This falls apart when you apply our (as in, the players playing the game) morality, because we see it through a fundamentally different lens. The vague and aloof notion of some higher 'universal good', which in itself is a binary interpretation, is a dangerous concept to apply. If there is a higher good, then all others are fundamentally evil because they are not aligned with it.
So on, so forth.
I don't think Kayle can make up with Morgana because they are too far committed to their causes. Old wounds left in the soul forever, words spoken that can never be taken back, etcetra ... The only end to their feud is the death of the other, because their grand plan has no room for the opposer in it.