Saying YES when you're supposed to say NO comes with consequences. And one of those consequences is that you're being tossed around like a wild wind, you can't stay incharged, you look careless and completely indifferent. And that's exactly what happened to your classmate when you said this....

"That attitude though came at a cost, which in her case was that she had troube to say "No". It hasn't existed much in her vocabulary, because sometimes that has the effect of being rude....."

It's quite unfortunate she had to face some of those consequences