Wedding speech by foreigner at Chinese wedding. Do's and don'ts

I am British and have been asked to give a speech at the wedding of my Chinese Admin (work colleague). I hired this young woman and we developed a close working relationship. She is like a daughter to me and I do not want to screw it up! Some advice please on what is appropriate to say and what is not. Do I follow the western wedding speeches telling some amusing stories or do I keep it formal? I have met her parents and fiancée and they are very excited that I have agreed to return to China for this special occasion. Thanks in advance. Susan