Ever since I am friend with this person I have not been able to see her online, my message take at least half a day to being marked as delivered and are probably not since none of them have been seen. I have never contacted this person before and have no problem with others friend.
There's a little icon with a tick if it's been delivered, and it changes to their profile pick if they've seen it. Does this "friend" logout of facebook when they've finished reading? Are you communicating with a sockpuppet or catfish? What do you mean by "I have never contacted this person before"? Are you spamming? Is there a chance you've been blocked?