Self harming worry

Hi there, I am new to this forum. My granddaughter is almost 9 years old and waiting for her diagnosis for autism, it is thought that she might have Asperger’s. Just recently she has been getting very anxious and has started  hitting herself in the head if things are not going as perfectly as she thinks they are supposed to, for example she was building a Lego project and stumbling over a part of it but her frustration was so bad she began punching herself in the head. My daughter is extremely worried about this and she’s a great mum and calmed my daughter down and everything was fine but my daughters concern is that can this type of behaviour  in the future turn into self harming in a larger scale. My daughter also has a seven-year-old son who has autism and her daughter is wonderful with him. Such a loving little girl and it’s very stressful to see her getting so anxious. My daughter is always looking ahead to try to help prevent  things happening and keep the children safe as we all do with our children and  love ones. I’m reaching out to this as my daughter is becoming anxious herself about this becoming more serious as my granddaughter gets older as she cannot get any information from anywhere concerning this.