That should serve as a wake up call for those dickheads. She clearly pointed out that she was aware of what they were doing to her friend, that it was wrong and that she didn't like it. If they want to stay in her good graces, they must stop that jealous bullshit (or at least not do it openly). Seeing friends stand up for each other is always great to see in manga.
Her confrontation was cut short by Umi (allegedly) winning the jackpot, but I hope that at least causes the pricks to lie low for a while if not outright solving the problem. I didn't catch this at first, but if Umi lied about winning just to get to be by his side... that's a lie I will willingly turn a blind eye to. Umi knows what she wants. Go for it, girl!