I know Otto was the one cheated but Marisa could have told him what he was doing was wrong and might harm the team at the end when she heard what Otto told her they got that lychee box free in front of the korean supermarket. Instead of making things right, he told on him to the judge hours later. Plus, she was the one who made that bad desert.
If she knew they haven't paid for that box of Lychee, she should have confront Otto right there and then or try to return that box herself as one of the team member. Imo, getting rid of Otto was just too easy.