The average college grad starting their first job (here in Kunming) makes between 2000 and 3000 kuai a month. We have a helper who works half time (20 hours a week) for 1000 kuai a month. Most chinese families would considerate unconscionable that we pay her a salary that is comparable with those who are so much higher in status (I have had this conversation many times over with neighbors, etc.), but we would consider it unconscionable not to give her a living wage, and with housing prices going up, up, up I think it is very important to keep the well-being of your helper and their family in mind. My understanding is that the going base-rate for helpers working for foreign families is 10 yuan an hour. I think this is a good place to start, and from there you can give a raise of 1-2 yuan per hour every 6 months to a year that she works for you. This is higher than the rate working for Chinese families, who typically only provide 6-8 yuan an hour but often also provide meals and/or housing.
One other thought—does this person have any other work? if not, could you possibly refer them to other foreigners who could hire them? I think you WOULD need to pay them more if they are only coming to your house a couple of hours a week. Ideally, you could set something up where your helper would have at least half-time work (20 hours a week) between yours and some other households. Perhaps she could do some cooking, or shopping at the market for you or some other tasks?