Exemption from HRT

How is exemption from HRT established?  My Polish client failed to complete the HRT forms for over a year due to language difficulties.  She was refused income-based benefits but it now transpires that she was under 21 when she had an accident and remained reliant on her parents (who are workers in the UK) beyond the age of 21 (as had no income), so there is an argument that she should have been exempt. Would exemption have been established only from the forms, or should she have been asked some questions before being sent the forms?