Indeed this may be the case.
Encouraging an underage child to put themselves in danger is very serious.
I agree with the word predator being used.
In your place I would be kicking up as big a fuss as is possible and as she has a child herself, see how she likes SS, and the police involved in HER life.
Whatever her motives, she will not have expected the blowback of SS and the police at her door and looking into her business.
I would be so furious at her actions I would absolutely make every effort to have her put in the spotlight for her actions and to make this as uncomfortable for them both as is possible.
I wouldn't believe her father that he didn't know they were in contact.
I would be letting his family know what has occurred and that it is now in the hands of the police AFTER the police have engaged with you, and I wouldn't hesitate in providing them with screenshots of the messages she saw fit to send to their relative.
She is one ugly person and the fact that someone who lives with her father clearly wishes her harm, means all bets would be off when it comes to making things really uncomfortable for her.