Sounds rather troublesome... hmm, what does she usually say first when she approaches you? If she starts with something common like asking how you or your son are doing, you could just answer "I'm/he is doing fine, thank you" and then before she can open her mouth add "Excuse me, I'm in bit of a hurry" then just walk away. A bit rude maybe, but since it's not openly insulting or anything she can't really do anything about it. If you really don't want to talk to her you can say it before she even opens her mouth. Another thing you can do is to tell her next time: "We're doing fine, but how about you? We always talk about me, but how are you doing?" then start repeating the questions she tends to ask you. When she asks something from you, wave it off with a short answer that doesn't really tell one thing or another and ask another question of your own. Won't necessarily work, but it just might bother her enough to get her to leave you alone for the time being.