You say "she has become politically more active", but I think it is more than that.
What you describe about her showing up with "a friend you had never met before", and lecturing you, and giving you a book about how bad your husband's profession is, etc.. screams "sect" to me.
I think it's scary as heck. She seems brainwashed and she is getting frustrated because you refuse to go along with it and "drink the kool-aid" or whatever.
People who think this way, don't realise anymore how rude and inappropriate they are being in their ways of trying to convince others to think the same way.
I would /not/ break off contact if you or your husband care about her at all, because isolating people from their friends and relatives, once said friends and relatives have made it abundantly clear that they are not the next willing victim, is exactly what sects want.
I would however put severe boundaries on what is and is not up for discussion. I would tell her she is never to bring that friend, or a different unknown-to-you friend with similar beliefs, to your house, and that your husband's profession is not up for discussion. Change the topic whenever she brings it up, cut off a phonecall or conversation when she does, be blunt and direct. And when it comes to your child, monitor her very closely.