Invitation letter and change of visa type in China

I study in China and I'll go to Iran to marry next February. I'm hoping my wife can come back to China with me.

1) My university claims I should give them a marriage certificate right now - which I wont have until February, when the university is on Spring festival holidays - in order for them to write an invitation letter for my wife to come with an S1. But your website says I myself can write an invitation letter for her. According to your experience, is getting the S1 hard when the spouse writes the invitation letter as opposed to the hosting institution? Would I be risking it if I bypassed my university's impossible demand?

2) Also, my wife is preparing her applications to enter my university next September and to the CSC scholarship. I imagine you can't be studying in China with an S1, and that it's necessary for her to get a student type, right? If so, can her S1 be changed into a student type from inside China since we can't afford two trips to Iran the same year?

Always many thanks for your kind and useful answers and help!