I haven't heard that before and it doesn't make much sense. Sleep is a affecting variable for many people. I haven't seen any evidence proving screen time. The less screen time the better in general, but I don't think for speech. You should also know most school based SLPs probably don't know much about stuttering. The majority of graduate programs barely cover it and if they do, they likely teach outdated information. So if she tells you things that don't sound correct or make sense, they probably don't. If you don't feel her speech therapy is helpful, it's probably her, not you.