OP, congratulations on both protecting yourself and trying to help your cousin!
We over at r/antiMLM are proud of you
This is good.
One thing people often don’t recognize: you usually don’t change someone’s mind immediately. You put something in the back of their mind that they will refer to later when something else comes up that challenges their position.
When her big paycheck doesn’t come and the Monat messaging tries to convince her to keep going, now what you’ve said will also be there to combat the messaging.