I would disagree. I don't think a pure spawn can become a Dual Spawn. You're probably either born that way or aren't, She would've probably went further along the path as the Body's new chosen tho. I also believe she would've learned how to incarnate as well, but she seemed to have messed that up. Now all she can do, in my opinion, is align herself to someone with superior power potential than herself as a fallen Chosen such as Jake, MC, Alice, Micheal, Evander, or Devana,
If memory serves right, Memory prefers Dual Spawn, but doesn't mind Pure Spawn. If memory serves right, Body prefers Pure Spawn, but doesn't mind Dual Spawn. All other apostles would kill you immediately if I remember correctly.
Ella is now destined to be another Chosen's or superior than Chosen ally. She's lost self determination power due to not being able to incarnate like Syla. She probably never would have anyway.
She shows that she completely disregards any opinions or duties others place on her period. During her last evolution, she's shown telling either the 3rd or 4th or both, "No. I don't listen to you. You don't tell me what to do." What apostle would make her disobedient ass their Chosen?
They want the reverence that Indra or Valrav'n have towards their lords. The two most reverent are also seemingly the two most powerful Chosen at full power. Correlation or causation. I think both!
Like with any rational god, obedience means being given more power. Disobedience means less power. Ella just doesn't care and think she can align with or create something even more powerful than her progenitors. Maybe, she can! Maybe she can't! We'll see.