Well, your decision on where the landlord lives will be a finding of fact and must be based upon the evidence you have to hand.
Firstly, has the landlord given you an address where she is caring for the granny/sister? If so have you written to her at that address and did you get a prompt reply?
Has the Council Tax liability for the claim property been changed to that of the tenant? If so have they claimed a single person discount?
Whose name are the utility bills in?
Have you visited the property? If so, where are the landlord’s clothes etc? All packed up or still in the wardrobes?
Note down all the information you have, make a decision based upon it and record your reason’s why.
You can even try using CH/1786/2005 to support a “still resident” decision if that is what you do decide.