In many places, "home based" catering businesses are subject to the same or similar rules as a restaurant, including the requirements for a commercial kitchen and inspections by the local health department.
Your friend should get an attorney who is familiar with the specific locality where she/he will be located, perhaps even starting with the local health department to learn the general requirements before even talking to an attorney. Your friend needs to know at least enough to ask the right questions to make sure that the attorney is familiar with the relevant issues and is not learning at the client's expense.