Marriage between foreigners and the s1 visa

I am an American teacher currently working in China. I have a Work Z. My girlfriend is from Nigeria and she is currently studying at a university here in Dalian. She has a student type valid until January. We would like to get married soon in China next month. We would like to know if it is possible for her to get an s-1 when her current student expires in January. If she can, does she have to leave the country and re-enter, or can they change it while she remains? What is the application process?