Domestic to international transfer at Shenzhen Airport

My elderly mother will be flying from Taiyuan to SZ and then transfer to an international flight for South Africa. Will she have to collect her baggage and then check it in again when transferring from domestic to international flights? Both flights are with Air China.
If she does have to collect her baggage and check in again does she have to go to the main check in outside security/immigration or is there a special transfer check in inside immigration and security?
Unfortunately we have had bad experiences transferring with baggage previously. I would really appreciate an answer as my mother is very worried and I am too. Thank you.