Motives I don't think are always pure. You can have pure friendships, with less pure motives or actions within that friendship or relationship dynamic. If I am aware enough to know the benefit of an action, is it impure? Not to me. but I agree with what you are saying, she knew. but also, she played that as close as possible, she didn't talk about it with anyone. She didn't threaten blackmail. She didn't as far as we know seek special treatments from Yasmin. She just backed her friend up and cleaned up the mess.
but like you said, what the show excels in, is just showing these people as human as possible. It doesn't stack the deck for one character to be good, and another bad. That fight at the end was painful. I don't see a right and wrong, I see two complicated people.
also, the show is probably softly nodding to class/socioeconomic tension, in how we perceive things. Harper has the lower status chip on her shoulder, it colors her worldview, I relate to that some level too. Yasmin has the elites worldview, and values things like friendship and loyalty, because the rest is (or was) all taken care of. Her world is secure. People like Harper are out of blood, because they see how cold the world is.
Yea the game is the game IMO. Harper is a TRUE piece of shyt, but Yasmin should only blame herself. We literally saw Harper not want to use Yasmin in that situation but her hands are tied and the money always comes first in their line of work.