Employers obligations on flights - advice needed

Two years ago I employed a helper who was already in HK. She had completed her previous contract with another employer and came to work for us at the completion without exiting HK – she was keen to do this.
After 1 year she took a holiday (she was required to exit for her visa) and I paid for her flight out of HK, she paid for it to return.
Now her contract is about to expire and we are both happy to renew however I am confused by what flights I owe her.
Is the employer responsible for the flight in and out of HK, or just one way for each contract?
What about in the situation that the contract is extended is the employer responsible to provide two new flights.
I am happy to compensate her as I value her contribution but want to know what my statutory obligation is first.
So far I have paid just one exit flight.
Many thanks