I would call the police, maybe not to press charges but to at least file a complaint. Some people are clueless -- she may need a call from the police to fill her in on how unacceptable this is. On the other hand, she may be crazy or a serious threat to any other children and should be on the radar, so to speak.
Technically, it's attempted abduction. That's pretty serious.
Your daycare provider did an awesome job. If I were her, I'd be worried about the safety of other children, and after hearing from you (and realizing this wasn't just a miscommunication or mis-guided relative), I'd probably call the police too. I would be worried for the safety of the other children in my care. It only takes a second for a child to disappear.
