My Chinese national fiance and I are planning to marry in Thailand.

I have a visa retirement extension which I renew annually in Dec. She has a 60 day tourist visa.

After we present all the proper certified documents at the local amphur to get our marriage license, what will we need to do to make my new wife a dependent on my retirement extension?

She will have to obtain a non immigrant O visa entry which I believe will require visit to Consulate in another country with copy of marriage certificate and your passport/extension of stay. Believe after 60 days here she applies for dependent extension to match yours. As this is an unusual situation I would suggest you ask at Immigration immediately after marriage takes place to confirm.