Thank you for your question
My name is Clare
I shall do my best to help you but I need some further information first
Was the agreement that they would pay evidenced in writing - maybe a text or an email?
Can you ask her - it is important
How far has the financial part of her divorce reached?
Your daughter can use the Money Claim On line service to sue her former in laws for the money based on their promise to pay
She shoudl sue them for the full amount outstanding.
She should also contact the Child Maintenance Service about maintenance for the baby
I hope that this is of assistance - please ask if you need further details