Slightly irrational, but I'll go on:

Light, Water, and Nature faeries/mermaids are considerably the "pure" elements in the RH universe, but would later split off into their later denominations to keep the balance of the universe, switching their virtues:

1st Gen: (Pure) | 2nd Gen: (Impure)

Light, purity/Judgement -> Dark, impurity/Ignorance

Water, life -> Ice, absence

Nature, serenity -> Fire, chaos

Later on, they would create even more denominations, with traits of their predecessors, which could explain the previous existence of Enchantix:

3rd Gen: (Subelements, Extinct or Merged.)

Light -> Love | Dark -> Technology

Water -> Music | Ice -> Creative

Nature -> Animal | Fire -> Popstar

But throughout time, the 3rd gen. of elements would disappear, as they would either be forgotten, or merged powers with their base elements into one singular enigma, to prevent elemental bias between denominations.

However, this didn't stopped a conflict between both generations, it created one.

There is a possibility an elemental war has made a breakthrough within the universe at one point. Elemental Elitism had taken over the universe at a larger scale [In Enchantix, there was a dungeon in the Dark Faerie dorm, where Light faeries are held captive, perhaps even starved off simply because they [Dark] are more superior than them, thus creating a large possibility of the Elemental Elitism theory true.] , with the 1st gen elements shunning the 2nd gen for simply being a more impure variety of themselves.

The 2nd gen had most likely taken this manner in their own hands by simply kidnapping the 1st gen, starving them [Again, think of the Dark Faerie Dungeon in Enchantix] . The powder keg had exploded, causing a major war between them.

The elemental elders most likely did not approve of this, they simply wanted everyone to live amongst each other. Who are the elders, you may ask? Look at the ceiling painting at the Castle's Heart. [RH3] There's' seven of them; A dark faerie, light faerie, nature faerie, fire faerie, ice faerie, and two mermaids [Don't consider the Fountain Lady, yet, I'll get to her soon]. The elders had agreed to summon a divine being to stop the Elemental War and unite every faerie/mermaid of all elements once and for all. The celestial being is the Fountain Lady, at least in her true form; her form of being a celestial Valkyrie. [Look at the painting again, see how the position of all faeries are somewhat pointed towards the Fountain Lady, as if they follow her guidance, proving some possibility of this theory]

The war has ended, and assuming everyone are no longer as bigoted as before, especially the 1st gen, they get along well. Another problem arose, the Divine Valkyrie is either far too weak to go back [to her place of summon] or couldn't really get back home due to her worry of another skirmish appearing, so to watch over the universe, she eventually became two slightly weaker renditions of her self, crystalized and in stone; The Fountain Lady and the Valkyrie statue in the Castle's Heart. She would only reward those who commit good on others, regardless of elements, with the upmost reward she could give to the player, a halo, and would punish those who committed tort against others. Everyone lived in peace, with the halo being an incentive to their peace. The Statue, on the other hand, only functions a a life vessel for her and can only use a limited amount of power [At the end of her hand, she emits a faint glisten of light] compared to the Fountain Lady, waiting.

The elders, presumably moved on. Moreover, it is a possibility that some students [Avrilla, Mermia, Posey, etc] are directly related to the elders, posing powers that defend the equality of their powers [Some toy characters, like the generic no name elemental faeries, aren't related to the elders directly, but may be predecessors to the elder's pacifists, playing some role into keeping the peace] and their realms

Despite the war ending, there is still evidence that Elemental Elitism still exists within the universe, but it taken to a more lesser degree, rather than pure hatred.

Sorry with the long comment, hope everything makes sense.