When is being nice being manipulative?

My friend says that I'm "phony nice" to get what I want. She says that I use niceness as a way to manipulate people, and that she's SICK OF IT, and I should "get real". I argued that I'm nice because I care about people and I control my emotions. I don't understand this...how can I know who is right? I feel authentic, she feels I'm phony, and she becomes enraged. Actually, I do hold back some because of her rage.