Treat her like an acquaintance. Respond cordially and if she starts to rehash old issues, tell her you want to remain on the subject at hand. If she persists in instigating, tell her you're going to hang up and end the call.
I wouldn't change anything with the bills until consulting with a lawyer, especially if it's causing financial hardship for you. Just let her know that you're not prepared to do that until you've spoken with an attorney.
