It's great to have some insight on Ella's mind, since even though she is such an important character, most things regarding her remain a mistery.
1. Ella knew she would lose the battle of the diamonds, so it wasn't a reckless move, and the fact that she wanted to be the one to fight Nyx shows that somehow things are still according to her plan, even if it means her dying in the process, but more than that, dying especifically to Nyx is what she wanted.
2. Tanos joining SIN seems very recent, Eisheth says that he is willing to join as soon as Ella calls as she is preparing to the battle, so she (and SIN) weren't cooperating with him most of the time.
3. She is convinced that Aglaec is more than a match to any of the people of HERO involved in the battle including Nyx and surprisingly Malik, she aknowledges that "those three" make it impossible to beat HERO yet Aglaec was supposed to be able to handle even him.
4. Ella being sentimental is not something i ever expect to see, but maybe the idea of actually dying makes her a little more emotional, enough to want to meet Mc one last time, really i can't wait for Mc to use the key and unlock his memories because i really want to know what the heck happened with those two.
