my mother-in-law renewed her ID card this year after being resident in the UK for about 30 years. They have recently been changing the old laminated card with new smart cards and were doing oldies on a year by year basis.
For people who reside overseas I think there is some leeway given i.e. if they haven't been able to make it back for when their particular birth dates were being processeed there is no need to rush back to get it done immediately. But once she returns she will have to do it within 30 days.
She needs to come back to HK for a few weeks. Book an appointment with ImmD and go along to have a new photo and thumbprint done. The new card is issued a couple of weeks later.
more info here:
http://www.smartid.gov.hk/en/replace/outside_hk.html