Talk to your principal broker to see if you can represent her in this transaction without compensation.

Be careful how you proceed here. If you advise mom on how to conduct this transaction and the buyer finds out, you may find yourself in trouble with your state regulatory agency. Either be in it or out of it, don't go part way into this transaction. It would be in her best interest to disclose that her daughter is a MO licensed Realtor, just in case.