I used Josie James Personnel:
info@josiejamespersonnel.com
2377 1598
I believe if the helper has completed her two-year contract, then she is allowed to remain in HK to process her visa and does not need to return to the Philippines.
As long as she has all her paperwork, you could probably start processing while she's still working, to speed up the process.
Anyway, you're better off asking an agency because they'll know all the answers!