If the mother insists on formula feeding, then extra care needs to be taken as there is a risk of introducing infection in the baby.
Cleaning the equipment
The equipment whether the bottles/ shields need to be cleaned after every use.
It can be done by immersing them in hot soapy water for at least 30-45 minutes each time and then cleaning them with cold water.
You can sterilise them and use immediately. Or if not used in next few minutes, then you may have to sterilise again.
Always follow the instructions on the equipment