Application form - signing

Hi there. I've invited my mother to come visit me in Beijing, however she's broken her hand and cannot complete the form. Section 7 shows that someone can complete the form on her behalf, however the Perth Consulate website states:

"(iii) Whether applicants come to the Consulate by themselves or consign others for the visa application, the applicant should sign on the application form (except the under-16-year-old children). Any information correction by the consignee is supposed to be confirmed by the applicant."

My mum has a cast on and can't sign her name.....is her signature mandatory?

Thanks....