Please send your wife the copy of your passport, Chinese residence permit and an invitation letter, your wife can try to apply for Student Visa as dependant, however, maybe the visa officer just issues a single-entry tourist visa to your wife rather than Student Visa as dependent. Your wife needs to submit her passport, one passport photo, one filled visa application form and the marriage license. If she just gets a single-entry tourist visa, she can apply for extension of stay duration at the Nanjing Exit & Enter Department.