a thick head co-worker

Still my co-workers have some trouble in their relationship and their daily communication. Ms.N, the temporary staff, is a tall, beautiful woman but not smart at all. And I don't know why but she trust me a lot, this afternoon she talked to me about the instruction she's got from her superior but couldn't understand. I had to explain her the purpose of it. It's good to be trusted by co-worker, but she seems to have no brains. In fact I'm talking with some superiors about how to fire her peacefully X(  This is just for the job, not for my likes & dislikes. Though I feel a bit like a hypocrite...