We have this family friend. She tells everyone she is my cousin though actually we are sixth cousins
She isn't very bright and can't pick up on hints. She "needs" to chat to people for hours and hours at a time. If I go for a walk and see her she will expect me to stop and chat for 1-4 hours - no exaggeration. She is on a mobility scooter so she gets to sit down whenever she wants through this. If she sees you she just latches on and it is so hard to escape her and her boring stories. The one time I said I was busy I had a phone call the next day, "I'm sorry I upset you." 
At the moment I am caring for my terminally ill dad and would like to be able to go for a walk whenever I want so I can clear my head and get some exercise. Also I suffer panic attacks when I have to stop and chat to people and I'd just like to be able to enjoy the walk.
How can I politely but effectively swerve this woman if I do see her out? Am I being a nasty rude b*tch? It's actually making me feel like a prisoner in my own home because I can never just go out without panicking I'll bump into her.