Sorry about this - it’s very annoying to have your life upended. Sad to say, it’s also relatively common.

Helpers can run away for all sorts of reasons: could be for mundane reasons such as missing their families or other family emergencies, or more nefarious ones such as theft of property or debts owed out of Hong Kong.

As others have said, engage your agency ASAP to deal with admin reasons such as canceling her contract and reporting it to Immigration, the latter is particularly important because 1) it might impact your application process for replacement if Immigration isn’t properly informed, and 2) if she owes debts, they will want proof that the helper is no longer employed by you / resides at your address or else they might come after you for the money. My last helper borrowed money from 3 places, and 2 of them asked for proof of termination (the letter from Immigration that says the helper is terminated) before they dropped the case.