I REFER to the letter ''Discriminatory treatment'' by Mrs Elsie Tu ( South China Morning Post, December 10). The wife of the Hongkong resident arrived in Hongkong from China on September 16, 1992 with a two-way permit and was allowed to stay as a visitor until December 9. On December 4, she applied for an extension of stay until December 16 the expiry date of her permit, in order to look after her sick husband. The application was approved. She was also advised to produce up-to-date information about her husband's medical condition if she required a further extension of stay to take care of him. On December 14 the wife applied for a further extension, producing a medical report indicating that her husband was in a critical condition. Although two-way permit holders should return to China at the end of their permitted visit and we do not normally grant extension of stay beyond the validity of the permit, her circumstances deserved exceptional consideration. A further 6-month extension was granted to enable her to look after her husband. TAMMY KEUNG for Director of Immigration