There is ADD and there are personality flaws. I doubt his behavior has much to do with ADD. But it's a good excuse.
There are lots of people with ADHD/ADD who are not lazy. Michael Phelps, the 16-time Olympic medalist, is a good example. My guess is that she kind of gave up and turned "lazy" quite a while ago.
I understand the frustration. Although my son lives in another state and wasn't diagnosed until he moved from our home, and he is now 33, and is on medication, it is always one thing after another with him - losing jobs, blaming others, etc. We have finally stopped supporting him financially because he would take our last dime, but every day is a guilt trip for me, a hole in the heart because I do not know how to make it better. If he lived with us, I know we would have the same situation you have. I know this because he once lived with his sister who ended up throwing him out because he let his dog ruin the sofa, and basically would not adhere to her house rules. I don't know the answer for you, but I do commiserate.