What's the best way to send money to someone in China?

Bank to Bank is as good as any. They charge a flat fee for International Transfers; �20-25 is the norm for a standard transaction. You can opt to pay all charges, so she will not have anything to pay. Western Union is quicker, but probably will cost more, as it is not a flat rate. The exchange rate needs to be considered, because some services will be better than others.