What would you do in this situation? Was I really on the wrong?

My daughter is in 9th grade so she’s 15. She forgot to take her lunch to school with her the other day so she called me and I said I could stop at Dunkin Donuts and bring her something. She asked if her friend could get something too so I said yes. The girls each got a bagel with cream cheese and a fruit smoothie. I took it to them and all was fine. Well the girls mother called me and bitched me out. She said that she had the girl on a diet to lose weight and the carbs I gave her threw off her daily count. I was really surprised because the girl is thin. I just couldn’t believe she was talking like that about such a young girl who is already skinny. I apologized to get her off the phone and to make peace because our daughters do cheerleading together. But I don’t think I was wrong. The girl is old enough to know about food allergies and restrictions so I don’t think I really crossed a line.