That is exactly who I was picturing in my head while reading this post. WOW! The only thing I can say is....1) don't let her "crap" get to you, perhaps that's all she wants. Maybe for some reason she is attempting to knock you down a peg or two. Don't let her....even in your mind! Keep strong when she talks with you.
2) rather than "taking it" respond to her with a "I don't care for this" comment next time she attempts to throw dirt in your face. Take the high road.
3) stear clear of her, be obvious...if she walks toward you at the school, pick your little one up and run for the hills like she's got the plague....maybe she'll catch on and find someone else to "rumor" too.
The hardest thing is ignoring the ignorance of some, if you figure how to do that......let me know!