Am I overreacting? Ex's girlfriend scolding my daughter

I feel like I'll be told I'm overreacting and maybe I am but it's honestly just the principal of things. I believe a girlfriend has no right to scold my child. What happened wasn't super big I'll admit that but it's usually how it starts. My daughter is 16 years old and my ex's girlfriend of 4 years was teaching her how to do her own laundry at the Laundromat because my ex said she's old enough. She ran into a boy and knocked his basket over by mistake and laughed a little because he was trying to pick up his underwear. She told me that dad's girlfriend told her not to laugh at people and what if that happened to her and she wouldn't want a boy laughing at her while she's trying to scramble her panties off the ground. I asked the girlfriend about this and she said she did say it but she was light hearted about it and just wanted to let her know it's not okay to laugh at people. I told her "Well she's my kid not yours. You don't get to correct her and the next time I find out you do I'll be in court so fast to change visitation." Maybe I blew up a little bit I just think it's the principal. You don't scold other people's kids.