Resignation During Maternity

I have a employee who has just utilised about 12 weeks of her maternity leaves and due to operational needs, she came back to work last week and she tendered her resignation today by giving us a one month notice. Pls advise what should we do with the remaining 4 weeks of her maternity leave?

Employee cannot use the maternity leave to serve as resignation notice period. She still need to continue to serve her notice for the next one month, the remaining of maternity leave will not be reimbursed to her.