Rescuing someone from involuntary commit to mental health place?

[ahaseurus]

It's a convoluted story - the gist of it is my SO's daughter was tricked by her father into calling 911 tonight. The father convinced the responder to take her away. Nobody will tell my SO where her daughter is.

What steps should be taken to - at minimum - establish where the daughter is being held and establishing communication?

Thanks for any clue how to "work the system."