If she got pregnant after she started employment with your daughter she is indeed entitled to maternity pay, although not at the rate you mention. This article is pretty comprehensive:
https://www.payefornannies.co.uk/statut ... y-nannies/
The key thing is that your daughter will be able to recover the maternity pay (although she will have to pay it up front). When I was in the same position they were pretty quick to refund me.
She is also entitled to return to THE SAME job within a year - i.e., she cannot demand, for example, to bring her child with her, unless agreed with your daughter.
Bottom line, your daughter will have to employ a maternity cover nanny, which I know is stressful and worrying if her child then gets attached to her, but there is no way around it.
If you are not using a payroll agency I would recommend using one to help you navigate through the minefield of SMP calculations and claim, maternity cover contract, etc.
Good luck - it’s stressful, but there’s plenty of lovely nannies out there who will do an excellent job as maternity covers and may still be around in the future for emergencies!