I had a thought: have you considered offering special discounts to colleagues? Where I'm from, some professions offer special rates to various groups like teachers, police officers, students etc. If you can afford to, you could adopt this practice and use it to win her over into paying for your services. (It may attract more persons to your daycare too.) If she continues to play dumb either way, then you'll have to decide whether or not to keep her as a client.