Not contradicting anything you're saying here or disagreeing - but they discontinued the term "ADD" back in 1987. It is now ADHD. If one doesn't show the signs of hyperactivity, it's ADHD-PI (Primarily Inattentive). I recognize ADD is common usage, but thought you or your SO might find it informative. Guessing she already knows since she reads a lot.
Yup, she's aware, ADHD is more of a mouthful and it really is not as accurate because so many people with it don't have hyperactivity. But it is the official abbreviation. The latest DSM also relabeled personality disorders as something else, but people still use the old terms. Asperger's Syndrome is also gone as term and it's now just part of the autism spectrum. Sort of like Pluto not being a planet.
Most women with ADD/ADHD are just the inattentive type. Another variation is whether someone is impulsive or not. Her ex-husband is her ex because he has a rather severe case that wasn't diagnosed until she left and he has both inattentive and impulsive, though not hyperactive. She is still good friends with him, but she said she can't live with that level of unpredictability.
For me I have some mild dyslexia and almost always mistype ADHD (I did a couple of times writing this). That particular combination of letters is very difficult for me to type correctly the first time.