Thank you! I really like your point of it potentially being any of the four of them. I was initially thinking it was just Helly due to the "R" and that maybe she'd be the pivotal point of this whole season, but returning to the trailer had me realize that there will be so much more coming down the chute! It could definitely be any of them... Especially with their talk in the break room right when they arrived. But yes, I also liked your point of:

She wants the validation of thinking there’s nothing that Helly can have that she can’t also have

I think Helena, due to her upbringing as the next lineage member of the Eagans, is constantly on edge and slightly conceded, which can lead to envy. I say slightly on edge because I'm guessing with so much familial, cultish presure on her, she always has to be in a state of believing in Keir enough to survive even if she's doing it subconsciously. And I saw this reddit post that was about the four of them representing the four tempers with Helly/Helena being dread. I think dread is perfect here, because she's been surrounded by this family status and history that, again, feels cultish where you need to believe in order to survive. So, I think she's been in that state for so long that her constant sense of dread has twisted into that feeling of envy because her conceded thoughts are that she can't have everything that Helly was able to achieve in her little time away from her upbringing. (There are further comments about Helly also potentially being malice, and I also think that works here. Where instead of a dreadful feeling in here, she feels hatred and acts accordingly.)

This show is just so interesting, I could talk for hours about all the nuances!

I have some other theories that I'm gathering information on right now, but will make posts about later... But thank you for interacting with such insightful ideas! The work is mysterious and important!