my guess is she would have to reactivate her HHR. It’s not hard to do, you go to the HHR office with the right paperworks and your passport with your entry stamp to do so.
The difficult part is actually finding a place that’s willing to let you register because 90% of all landlords won’t let you.
You do not lose your HHR permanently, you may get automatically “moved out” for leaving for too long but it can be reactivated anytime. However benefits like NHI would have to wait 6 months.