Rude neighbor with rude comments about my son...!?

Some people are just opinionated, ignorant and rude. If she's not causing you any undue trouble other than her rude comments, my advice would be to just ignore/avoid her. You can escalate a situation to where it can easily get out of hand if you engage in tit-for-tat insults back and forth. And, that sort of thing doesn't really do anybody any good. Be the bigger person and just ignore and avoid her. She's the one that will have to live with the natural repercussions of her anti-social ways. You don't need to bring problems into your life by making what was once just an unlikable, rude neighbour into an out-and-out enemy.