Do you own the property in your name or a business entity? If ownership is in your name, your niece will likely need to be licensed. If the property is owned by a business entity, its unlicensed employees may be able to manage the company's real estate. In any event, you should consult with a real estate attorney to review this matter and counsel you accordingly. These licensing issues can be tricky, and a violation can be charged as a felony in Florida. Don't take any chances. It's not worth it.
If this answer was helpful, please mark it as "helpful" or as a "best answer." The answer is based on the limited information provided and the answer might be different had additional information been provided, especially given the complexity of the law. Accordingly, this answer is for general education purposes only, and it neither creates an attorney-client relationship nor provides legal guidance or advice. You should consult with an attorney licensed to practice in your state.
Assuming the subject commercial property is located in Florida, so long as your niece is not receiving compensation or valuable consideration for the services performed by her on the property owner's behalf there is no licensure requirement under Chapter 475, Florida Statutes, which regulates real estate brokers and sales associates, irrespective of who owns the commercial property. Conversely, if your niece, as the property owner’s agent, employee, or independent contractor, receives payment of a commission or other compensation strictly on a transactional basis, then her licensure might be required, irrespective of who owns the commercial property, depending the specific services she performs.