Hi Holysmoke
If your friend is in hospital for four weeks or more then they must notify PIP that they are in hospital, their claim will stop, once they come out of hospital, they notify PIP they have been discharged and their PIP claim will be reinstated, PIP may ask for a copy of the discharge letter.
If you do not notify PIP they are in hospital, it will create an overpayment and they could get a fine.
Gary
Nothing on this board constitutes legal advice - always consult a professional about specific problems