S.S.
I had a similar situation with an in-home care but it didn't get ugly. Without your copy of the written contract, it would be difficult to fight if she does indeed take you to small claims. Regarding the tax ID number, if you are friends with any of the other parents you can get it from them, just tell them you forgot to get it from her and can't get her on the phone. I would file a report with the state on her as well, they will do an investigation. Not sure where the written ad was but if it's something like Craigslist, you can flag her ad and it will get taken down.