she would still have to pay around 600zl per month ZUS
In case of umowa o dzieło I think there's no ZUS (only income tax and NFZ), ZUS need to be paid in case of umowa zlecenia (unless It is already paid in some other way) however fixed ZUS payment is only for people running a company, ZUS of those employed by someone is a fraction of their income, so it's not possible to be employed and pay more in ZUS than the income...