So a little headcanon on my theory of how I think Cassidy and Domino feel about each other?
Domino and Cassidy are both very similar because they're both blonde, are elite Team Rocket members with matching uniforms and are both quite stuck up. But if they know each other, then how do they interact? (This is just fanfiction rather than a theory, but still read because it's fun to think about.)
I don't think that they get along very well, they might even be enemies. In Cassidy's case, she's her second archenemy after Jessie. Both Cassidy and Butch wanted to be Giovanni's favorites but Domino was the only rival within their rank and the fact that Domino was way younger than Cassidy and the fact that she pretty much met her match at that point, is what made Cassidy hate her especially when she acts like she's the favorite instead of her. And it's possible that many other agents and grunts were attracted to her and are quicker to look at her than with Cassidy.
Plus, Domino was assigned to look for Mew or Mewtwo and regardless of who she finds first, is good for Giovanni either way. That's another thing that makes Cassidy really hate Domino, as having someone younger than her taking arguably the most important mission of Team Rocket seemed wrong and insulting to her. Butch and Cassidy's failed missions are definitely part of the problem but they are still good at capturing Pokémon to sell to the black market (I mean just because we only see Team Rocket fail on screen doesn't mean that they always lose because if they did, wouldn't the organization go bankrupt and be disbanded? And wouldn't the boss fire them and possibly kill them? They couldn't just let them go, if we ignore Journeys as canon but that's a subject for another day.) but didn't succeed in the big projects and Domino slowly was about to replace her and Butch.
And vice versa; Domino hates Cassidy too but not as intensely as Cassidy does with her. Most of the time, she'll always come around her acting sassy, rude and condescending, especially after Cassidy thought that she was ahead of everyone else but the thing that she hates is that she has a handsome man like Butch for a partner which makes her feel insecure about herself and Cassidy knowing that, she'll always try to get on her case about it. She sometimes might try to split them up by starting conspiracies and frame them to break them up. But unsurprisingly, it doesn't last even if she succeeded and Cassidy gets the last laugh, causing Domino to grow bitter and take it out on anyone nearby.
In conclusion, I feel like they both see each other as a shady reflection of each other which is why I think that they'd hate each other. Because Cassidy could have other enemies besides Jessie and Domino doesn't seem like the type that anyone would make friends with because underneath that fake cheerful act, she seems like a pretty grumpy, rude and unpleasant person to be around even by Butch, Cassidy, Hun, Attila, etc but grunts would still hit on her which Domino would turn down very hard.
Thanks for reading! What do you guys think? Do you think that Cassidy and Domino would be friends, enemies or just not care about each other? Let me know. XD