In earlier episodes, Marty told Ruth he'd show her how to launder money so he and the family could leave for good, and Ruth could handle the businesses on her own.
Suddenly, we find that Marty hasn't told Ruth everything she needs to know. Marty's left out crucial information - which seems to be an easy procedure, once you know the steps. He told Navarro exactly how to handle the red flag, and could have shown Ruth, had he really wanted her to handle things on her own.
I guess the writers didn't want Marty to be redundant after all.