The requirements for tourist visa extension are similar as the requirements for China tourist visa application, but now it is not easy to get a tourist visa extension. Owing to the Asian Games, the China visa policy tightens, the Enter & Exit Department in Nantong maybe refuse to issue visa extension to your mother. You can know some information about Shanghai Tours(https://www.travelchinaguide.com/package/shanghai.htm) to take your mother to visit Shanghai and Suzhou.