I've just read your opening post OP and then further on when you expanded on your relationship with your aggressive neighbour. I'm so sorry, you sound such a lovely caring person, she should be counting her lucky stars to have someone like you around, clearly a kind and thoughtful person. She has been unbelievable cruel with her words, she won't be young forever, and maybe when she has reached her older years, her own nasty comments may come back to slap her in the face, I like to believe in karma. Quite honestly they way you describe she comes across as really base, conniving and selfish in the extreme, almost to the point of being unhinged.
Somebody upthread mentioned Age Concern I hear they do good work with older people experiencing problems. I know you don't want to involve your family but I think you should let them know how she has verbally abused you in the most horrific way, as for getting your children struck off from the dental practice where she works, as a receptionist, I doubt whether she would have the power to do that. There are many helpful suggestions posted here, I think you probably need to be a bit proactive in dealing with someone who is an absolute monster.
I wish you all the best and hopefully happier times