I'm split. On the one hand, we have freedom of religion and a parent should be able to try to bring up their child as they see fit. We can argue about the damage or lack thereof - many are happy with their beliefs (even non-JWs who believe nonsense).
But being ex-JW, I hate to see people indoctrinated.
The JWs bring their child in field service to teach them how to do it. Encountering negative feedback other than "I'm not interested" was uncommon for me. But if they want to train their children, their children should hear the comments that actually challenge their beliefs.
I remember when I was in my early teens. My brother and I went to some doors together and got invited in by a guy (I know, shouldn't have done that) who definitely did some homework on attacking the JWs. The argument was about Trinity, mostly. He also said there were more JWs per-capita in mental institutions than any other religion. Didn't know whether it was true or not. I don't believe it now because I think JWs would seek JW help for any mental issues instead of institutionalizing themselves. But to this day, I wonder where he got his info. That guy actually got me thinking the WTS kept secrets. He told me to look up something in a book at the KH library. Sure enough, it was what he said. I took it as a mistake, but the doubt started to linger.
Hopefully you have sparked something. It might not be realized today or tomorrow. But she may start to look into it when she moves out on her own some day. Or when she's in high school and thinks to look up some things on the library computer.
I do think throwing out the Satan card is a bit much. It's likely to throw up all defenses and block out your message. The thought of being the devil's agents is too scary for them to accept. So they will block it and your message. Otherwise, good info.