Well, you have experience with her and I don't, so I can't really say for sure but I am thinking that she isn't just rattling on and saying whatever comes to her head. She is telling a specific thing that happened, probably thinking it won't be publicized and when it is, she is in trouble with people for telling it, so she just publicly denies saying it. I don't think that makes her a pathological liar. It makes her just covering her butt. That is something any one of us could do. Haven't you ever told someone something and said, "If you tell anyone I told you, I swear to God I will deny I ever said it."
I don't know what is behind Darlie's mental problems, though I do believe she had some. I just read Ann Rule's analyzation of Diane Downs. I was hoping to find some of Darlie in it but I have to say I really didn't see much of Darlie at all. Maybe a little in her need to be the center of attention, but that was promoted so much by Darin and the people around her, I am not sure where their need for her to be the center of attention ended and her need for it began. One of the things I find scarey about Darlie's case is that she doesn't appear to be a psychopath or sociopath or even histronic or narcissistic to any great degree. Maybe she was just sooooooo swayed and ruled by material wants that she would literally sell her soul to hold onto them. I don't know.
But back to Darlie Kee, I don't see her as a habitual liar. I think Darin expresses some of that and that Darlie demonstrated some expectation that she wouldn't be held accountable for what she said (the letters from jail) so she was a little loose with the truth, but I need more to see Darlie Kee in a similar light. Got anymore bad behavior on her part to support your view?