Thats the problem with people. Feral cats are used to getting food on their own. When you start feeding them, they get used to it and will come around regularly because theat is what they've grown accustom to. When the person stops feeding them, they don't really know what to do for food since their old"hangouts" if you will, have already been overtaken by other animals who needed food. This leads to starvation possibly.

In my opinion, discuss calmly the situation with the old bag. If she refuses to see the light so to say, leave poisoned food on her doorstep. That will solve the problem.

/animal lover
//weed lover
///people hater