Archmage Transcending Through Regression - Chapter 148

I’m a little bit confused…
In the past… When the Founder was betrayed by her sister, didn’t she die? And then thw sister also died of natural causes? Then how come the elders were able to imprison her like that? And who is this Aither Elf? Whose reincarnation is she? Because the founder is reincarnated into this elf so what even is happening??? 😭