Dealing with Lies

So, for some time now I have been dealing with my wife and her ADHD. Lately I have noticed that we have been getting into more and more arguments by the week. The arguments always start off as innocent conversations. Somehow someway she redirects the conversation to something that has happened in the past. I'm not one for bringing the past up because it belongs where it is; in the past! When bringing the past up, the stories always seem to change when she she is telling it. She begins to tell lies about what actually happened and it pisses me off when she does it. She does this constantly and I don't understand why? Has anyone experienced their spouse and the lying?