definately read as much as you can, watch stuff online about it, borrow library books, join support groups, just inform yourself as much as you can. try and read up on healthy eating- there is a lot of info about carbs, omega 3 oils, etc- and exercise, meditation, martial arts, memory games, etc- all sorts of things that can help or hinder when it comes to ADD. it’d probably help your social phobia as well as your ADD to take a class like yoga, and you could probably persuade mum to let you do a martial arts class under the guise of learning self defence (every mum wants their little girl to be safe, and being able to protect yourself physically is a big part of that).
your mum might come around with time, but – and i know you’re not gonna like this but i think it’s worth saying- worst case scenario, if she just will not get on board- well, in 24 months or less you’ll be a legal adult, and you can make your own decisions regardless of what she feels or beleives. i know that feels like forever away, but trust me, it’ll come (and go reaaalllly fast, too). it might not seem ideal, but if you have to wait until then to get back to school or onto medication, you’ll still get there- beleive in yourself and remember how you DID learn to do those things you found hard as a kid, even if it took you a little while. 
if pushing and pushing makes her more and more defensive (cos that can happen), maybe just stop mentioning ADD, and do things that’ll help ADD, for other reasons… like with the yoga class- sure it’d help with ADD, but you could just omit to mention that while you’re telling your mum how it’s good for bone strength, focus, relaxation (aids in school work, exam prep, etc) posture, cardiovascular health, etc. i’m not advocating lying, but sometimes you have to be a bit selective with how much truth you choose to share. 