Nannies have always been able to work as it's not a job that can be done at home.
The government have been quite clear about this. Yes many nannies have been furloughed as parents did not require them or the nanny requested ot due to being vulnerable or childcare issues.
You need to have a conversation with your nanny and discuss the risk assessment for the work place.
Can she have a designated toilet, bring her own food and utensils. Can you provide gloves for use for changing nappies, laundry, etc. Soap in kitchen , bathrooms, disinfecting products.
Can the adults in the house, older children social distance? I'm thinking aged 10 plus for this. Do you have a home office?
Does your nanny travel by public transport?
Try to minimise the risk , you cant take it away all together.
If you dont need her I believe the furlough scheme is continuing to June , after that you would be making her redundant.