That's really tragic, and I'm sorry that happened to the two of you. It sounds though like there were undiagnosed issues at hand - ADD won't really give someone anxiety about speeding (if anything, it will cause them to do it more, either from hyperfocus on the task of driving or by lack of focus on the speedo).
I know amphetamines can also nominally 'treat' things like depression and anxiety, by dumping reward chemicals into the brain (but, as it seems happened here, also exacerbate a latent set of bad behaviors). You really don't want to make someone who's afraid of the world / mad at the world / frustrated with the world more motivated, which is the essence of how a lot of ADD meds work.
I know amphetamines can also nominally 'treat' things like depression and anxiety, by dumping reward chemicals into the brain (but, as it seems happened here, also exacerbate a latent set of bad behaviors). You really don't want to make someone who's afraid of the world / mad at the world / frustrated with the world more motivated, which is the essence of how a lot of ADD meds work.