You have already identified the problem - 'manipulation'. Dealing with it should not be a problem - your soul knows all. Just listen to your inner voice and do those things which are fair and doable and don't do the others. Be very polite when saying 'no' and don't give any reasons - just say I will not be able to do this. That's it. No need for any justification. Don't feel guilty, because that is a psychological plot to 'manipulate'. The more you get manipulated the more you raise expectations in the old lady. She begins to feel it is her right and she will 'manipulate' your feelings accordingly. Just become a witness and deal with issues in the moment. All the best. God Bless.