It's almost an hour past my bedtime but I finished this.
This is Queen Titania, current leader of the Lost Ponies.
When a new leader is chosen and fused with the crystal they become virtually immortal. They don't age, get sick and have advanced healing. If they get critically hurt that part gets replaced with crystals. But they can still die. If enough body parts get replaced by crystal they get the urge to return to the crystal caverns and... assimilate, become one with the crystals again. Decapitation speeds up that process immensly.
The crystals posses some sort of conciousness, giving the current leader.... not exactly advise, but suggestions. It's a sort of symbiotic relationship.