It's a complicated situation but I see two things here.
First and most important is she wants to take off somewhere else and take your child with her. That's the plan. Only you can stop this in its tracks right now.
If it were me I'd be in the car heading for State C to pick him up today.
Second, seems to me she is just up and leaving (perhaps to a more enabling environment?)
Have you consulted a lawyer at all?