Her bringing in the police means exactly squat. It's a civil matter, not a criminal one. The police can't DO anything. There'd have to be a court hearing after filing a complaint with the legal system, to determine ownership of the animal.
So you just wanted a good home for the pony? I wouldn't be inclined to GIVE someone anything after they threatened me with legal action, and tried to tarnish my reputation. I'd have called her bluff, and told her I'd see her in court. That is, if I wasn't trying to pull a fast one, and got caught.