How to deal carefully with someone with ADD?

So I have a roommate with ADD, she s very mature, successful and hardworking, however being her roommate can be trying at times. 99 percent of the time we get along great and communicate well, but there are things where we just can t get things across. Like when I say something she interprets it in a different way. For example yesterday she was saying she had not really driven alone and I told you can practice driving alone so you can get comfortable, but she took it as if she didn t know how to drive. Couldn t explain what I meant which was to get used to driving alone, not that she can t drive! Today, I felt I blew our friendship as she offered me to have a burger she got from a restaurant after showing it to me and I for some reason took a different burger.I was busy, tired and stressed after an exhausting weekend so my mind was weary and thus totally forgot what she had shown me, but I can tell She found out and I felt she was frustrated and mad. I apologized to her, and she said it s ok but that she doesn t "get" me after she said she showed me the sandwich. I just did something without thinking..it happens but I was so tired and weary. I do admit I felt stupid and horrible. Is it me and how can I deal with her?