First of all, you must check it out the domestic helper's performance from her ex-employer. Why didn't her ex-employer renew the contract with her? Fainally, if you realize the whole story and the last decision still want to employ her, then...
1) Procedure
It would be better to give a ring call to immigration department hotline, the staff will teach you step by step rather than I teach you, right.
2) Fee of charges
Visa Fee, contract fee and Re-training Fee (HK$400 x 24 months)
3) 須留意事項
I think you should ask Immigration Department if the domestic helper need back to Phillipines first before start the new contract or not.