Vietnamese national travelling to Hong Kong for 3 day trip

Joe, you needn't apply one in advance because you enjoy 90 days free stay there. For your GF, she should apply from HK Immigration Department directly. She should post her application to the department. To apply for a visitor type, she should provide her copies of her passport, previous entry records (if she has), filled application form, passport photo, flight itneraries (round-trip air tickets), accommodation booking and financial standings (employment certificate, recent six months bank statement or salary slip). It takes four to six weeks to deal with her application.