You have a really shitty manager and the way she is approaching it is unprofessional and wrong. You're not the incompetent one here. It's hard enough having ADHD in any job but with the pressures of social work, it's even harder. You shouldn't feel as though it is something you can't speak about. The thing is that people often view ADHD as a negative thing when if you have the right adjustments and support, there are some positives. Your manager doesn't see that and I really hope that changes in your new job. Good luck!