Is it still nice?

We took the kids to the school the other night to play on the playground. While we were there another little girl showed up and she started following M around. M doesn't like to be followed or copied and so she was getting really frustrated. M went down the slide and then started climbing back up the slide but who should be at the top but that same little girl so M tries to go up the adjacent slide but the little girl moves over to that one. Whenever M tries to climb up one side the girl follows and by now M is really upset. I went over to M and told her that if she asked the girl to move that perhaps she would. So M says, "Will you please move, dupid (stupid)?!" I'm not sure if it is nice if you call the person stupid even if you say please. I couldn't help but laugh as we have tried to tell M to not call people stupid but it was just too funny when she said it looking up at the girl that had followed her around.