You should contact the immigration department, where issues her working visa or the labour department .
Normally, you have to pay her one month in lieu of one month's notice if she has passed the probation period stipulated in the contract. If she has not passed the probation period, you have to give her 7 days notice or 7 days pay instead.
I do not have the phone handy but you can check with telepone company by dialling 1083 for cantonese or 1081 for English to find out the telephone number of immigration.