Showing appreciation/giving thanks

I was dating a girl with ADD and one thing that bothered me was that she very often would not say "thank you" or show appreciation for dinners, gifts, doing nice things for her, helping her with her school work, lending her things, etc.  It was something that really bothered me over time because I felt like she was just taking advantage of me and it caused me to close down quiet a bit.  I raised the issue with her and although she acknowledged what I said, she seemed not to really change her ways.  I told her it made me feel like she didn't care about me.

Anyway, I didn't realize the impact of ADD at the time of the relationship and I have only started reading about it now that we have been broken up for 2 months.  I don't talk to her anymore but now based on reading about ADD symptoms and understanding her behaviour better (anger issues, impulsiveness, etc) I am open to being friends with her again down the road.  One thing that I still don't understand is whether or not there is a link between her lack of appreciation/ saying "thanks" and her ADD.  I am seeing it as her being so focused on the enjoyment of the meal/movie/whatever that she doesn't realize/observe how she got it and doesn't think it is important to say thank you.  I posted this on another ADD forum and a few people with ADD said that they are struggling with the same issue.  However, on here I saw a thread where people were saying that their partner was VERY giving, empathetic, generous, etc.

Any insight would be appreciated from both ADDers and Non-ADD partners.