Idk, I feel like she isn't very simple minded. She is very calculating, thinks about her enemies and their motivations. Creates elaborate plans that factor in the larger picture as well the immediate consequences. She makes very sound conclusions and is shown to have a constant running internal monologue about things and even thinking through how it logically makes sense to wipe out this branch of the assassins guild because it helps her new master, helps her, and helps a future where she might need to kill someone for her princess friend she made.
If anything I would think she is an overthinker because she takes very few actions on a whim and is constantly weighing cost benefit in a given situation.
She is super simple in terms of her life goal of, "I don't want to be controlled and be a puppet" but all of her actions support that life goal very intentionally