Tell them. It's a symptom, and if they are to help you, they should know. If your mum already knows you were self-harming, this won't be as hard for her (imho). Perhaps you have been using it as an alternative coping strategy? You should tell your CAMHS people so they can consider whether to sign you off or not. Take the opportunity you have here, please. Well done for not self-harming for a while; tell them what you've been doing instead, please.