She sounds so lonely. Is there a senior center nearby where she can meet some other people. If not, have you tried saying "No, we won't drive over to put in a light bulb or take your groceries out but we will call you on the phone and talk once a day" (if you can spare the time). Loneliness is an awful feeling and I can only imagine how badly she feels having to come up with such feeble excuses to have a little company. That doesn't answer your question but it's what came up for me. Take good care of yourself first, then take care of her.