You may both be right. There is an increasing amount of scientific evidence that screens (TV in particular) and junk food (sugar and saturated fat in particular

You may both be right. There is an increasing amount of scientific evidence that screens (TV in particular) and junk food (sugar and saturated fat in particular) are severely impairing brain development in children, leading among other issues to difficulty to focus and ADHD. So yes, keeping children off screens as much as possible (+ healthy food + sport) looks like a good advice. However, when you have this condition as an adult... well, there is some level of plasticity in the brain, but it looks harder than just "change your behavior", it may be required to also treat the symptoms.