There is a stigma that goes with having something like ADD, however, you can't control what other people think. People can be very shallow, ignorant judgmental and narrow minded. I think many parents are more concerned about what their circle of friends might think if of them if they had a child with ADD. I'm only 53 but in my parents generation and before you never talked about going to therapy and you never talked about your feelings. Back then if you acted differently you were considered "feeble minded" a moron. You were put in an asylum. Society was very cruel to people who were "different". In some cultures, even today, having a child with some form of disability, physically or mentally , brought shame on the family or it was a sign of the devil. The child was discarded, sent to an orphanage and disowned. Peoples religious beliefs have a lot to do with dealing with mental issues.
What your friend will at some point realize is that having ADD and making an effort to control it won't be as much as an issue as having it and not doing anything about it. People will judge her for her actions. One thing I notice about people your age, and I was there at one time, is that you worry way to much about what other people think of you, nothing wrong about making a good impression but kids try to hard to fit in an be accepted. I notice it more with girls especially when a guy is involved. Social Media is no help. In fact Facebook has had nothing but a negative effect on society, all it has done is make billionaires out of it's investors. People need to realize that your posts, pictures will never go away.
Today there are options to treat ADD unlike when I was a kid, your friend is at an age where she can make her own choice and her decisions will either lead her to failures or success. Unfortunately, a young kid doesn't have that option, no voice, he/she is at the mercy of their parents. Somebody in your friends family saw something that led them to get her tested, now she knows the reason for some of her behavior, but knowing and ignoring it is only going to make her life more and more difficult and for those around her. There are several books about ADD in women written by women who have it. Maybe it might be a good idea to either give a copy to her mother to pass on to your friend or leave for your friend for her to find, not telling her that it was from you and walk away for a bit. Her boyfriend maybe playing a big part in her behavior and their isn't much you can do. She'll learn the hardway. As I said I work at a college, and I found out very quickly that the study they did that said girls mature much quicker than guys was very true. Young guys today have absolutely no respect for women, they are basically @$$h0le$. When I was at that age we never treated women the way they do today.