If she is minding the baby in your own home then effectively you are her employer. So you should be paying her minimum wage and also PRSI. If she is minding the baby in her own home then she sets her own rate and is responsible for making her own PRSI payments.
She won't be entitled to any Social Welfare benefits because she is not unemployed (as she is on leave from her own job) and also she is not available to seek full time work.