How do I deal with a narcissist "friend" with adhd?

My friend always says she's sick. She does it for attention. She's insecure. She ditches me for other people and only wants to do things when it's convenient for her. However, it's not this way all the time. She and I have had many good times, many laughs, and many discussions about life. I don't know how to tell her that things upset me without her getting defensive. Sometimes she fails to see that I need her advice, input, or empathy. What doesn't make sense is that she is needy towards me. If I try to distance myself from her, she becomes clingy. She says she doesn't know how to be a good friend, and that she's never had any real friends. She fails to see that some of her actions are hurtful... I have done a little research on narcissism, and it says not to try to argue with them or point out a wrong. If I try to tell her she has hurt my feelings or that I don't want to be lied to, she cries and becomes very nervous and changes the subject. There's something going on with her, and it worries me. I'm emotionally exhausted by this friendship sometimes. I don't know how to deal with it, now that I'm aware what the problem is. Narcissism is more than being selfish. It's a deep desire to be wanted and stems from emotional disturbances or issues from childhood. Narcissists are willing to do anything they can to feel important. How do I tell her she has seemed selfish and has hurt me without being mean about it? Is there an inoffensive approach to narcissists? I don't believe in doing the same things to her that she's done to me. I don't believe two wrongs make a right. Are there any hints I could give her or things I could do to make her think twice about things? Again, I don't want to cast a stone at her and be bitter or get revenge... I don't want to cut her out of my life, but I want her to realize that her behavior and social skills are not ok. Btw- she has adhd as well.