Another idea, if you are concerned that the counselor will tell your mom, go in and have like an interview session with her. You should ask about informed consent and your rights to privacy. Ask her if you decide to work with her if she has to tell your mom. Ask her what you can say to her with out her going to your mom or other people. She will likely say that she will break your confidentiality if you poses a serious threat of harm to yourself or others. Or if there is child abuse/elder abuse going on. Ask her what constitutes as "harm to yourself". It may be different in South Africa but that's how it is here in the US.
Take the time in that first session to get your questions answered without telling her everything. This way you can decide if you like her and you can determine if she is safe.
But please do seek help. Three years is a long time to go without proper support. Think of this as an investment in your longterm health. I know you don't want to put added stress on your mom but you are important too. You don't have to struggle. Help is there.
Let us know how it goes!