Wtf. That's exactly the reaction I've got at OPs daughters age (12, she's not 11). And from a nurse, no less. In front of my class.
We had to queue and were weighted. I went after a petite girl and the nurse exclaimed, wow, what a BIG lass you are! And proceeded with advice how to lose some weight, because 57kg is A LOT for a girl.
Why didn't she take into account that I was 1.8m (5'11 I believe) and my classmate was about 5 foot nothing, I have no idea. I was slimmer than the other girl, just weighted more because I'm tall (reached my full adult height at the age of 12)
I weight 55kg now and I'm a small size 6, slightly underweight, not overweight. So it depends on height.
My DD is 12 now, 5'4'', weights 54kg and her BMI is 20.4, she's not overweight at all.
I'd complain OP, yes. YANBU.