Hi Mushi, sorry I should have clarified that the situation I mentioned above ($460, no need for airticket) applies only if you rehire you current helper (i.e. advance contract renewal) and NOT if you fire the current one and hire a new helper. If you change helpers, then course you would have to pay for a ticket home for the old helper (and pay for the new helper's ticket as well).
I think it's quite straightforward to do the advance renewal yourself. You can downlaod all of the forms from the HK Immig at this link (except for the green contract which you need to get 4 orig copies from Immig - but yr helper will be able to do that. Most helpers keep a stock or can get from their friends).
http://www.immd.gov.hk/ehtml/fdh_acr.htm
If your helper is from the Philippines, then just download the express contract processing form from the consulate website, and then get your helper to bring it to the consulate together with 4 signed orig contracts to get it notarized.
http://www.philcongen-hk.com/labor/main.htm
Your helper can then take the notarized contracts plus all of the Immig forms and supporting docs to Immig tower in Wanchai to apply for her new visa.
My helper was a Direct Hire so I did all the documentation myself when I first hired her. The renewal process seems a bit simpler, and she can probably do all of the running around herself, without needing you to go.
Mushi, if your helper is confused/worried, I think she should talk to her friends on her day off. They have very good networks and I'm sure they can explain to her how to go thru the whole application process.