Can I ask the nurses in the hospital to feed my newborn with my sister's breastmilk as I have very low supply? Anyone here has tried that before?

I guess hospital will not allowed you to feed donated milk in hospital due to protocol e.g. safety reasons (hygiene, health risk from donor and etc.). What more your baby is still a newborn. Donated milk is not so popular in Singapore yet. Lactation consultant will encourage you to latch more during the hospital stay instead. In addition, newborn (1-3days old), their tummy size is very small and does not need to take in a lot of milk and thus, you do not worry if you have little supply. Nurse will feed your baby with formula milk if you do not have any supply at all during the hospital stay.