Probably sebaceous cyst..Not yo worry..For detailed information do direct online consultation by sending photos

If the cyst is not troubling your mother, you can let it be as it is. If there is any pain or pus within it, it indicates infection, which needs to be treated with antibiotics. You have to watch out for change in colour and sudden growth of the overlying skin, because that may indicate a cancerous change. Dermatologists can excise the lesion safely if it is within or under the skin, as long as there is no deeper involvement with the brain tissue or skull. The reason for referral to a plastic surgeon was probably for removal with minimal scarring. Homeopathy will not be useful since a surgical treatment is required. Kindly share the photographs of the cyst via online consult option and I can help you out.