Start her on antibiotics to reduce infection and inflamation, the dentist will do that anyway.  Amoxicillin 250, two capsules per day, one at breakfast and one at dinner time will be good, prescribed to me about 9 months ago on a similar matter.  20 capsules sell for 13 Rmb.

After inflamation and ahche is gone, then cavity can be fixed, even root canal done if needed.

I used to go to dental offices, but they did work on a schedule and charge per visit.  So, I discover that locally, People's Hospital on 5th Floor has a dental clinic whee all graduates of dental school must practice for 1 year under close supervision of their teachers.  Their charges are reasonable (cheaper than at other places), and at least here, they are darn good !.  Check if Guangzhou has similar set up, please.