and how old is this child?
What I see here is the need for custody orders. If the child entered the United States with her, then the child will probably be able to leave with her again without too much difficulty unless there are court orders to the contrary.
You should probably seek out a family law attorney in your area for an immediate consultation. . . . and for immediate filing of a paternity complaint to establish your parentage. . .
Let me know how it turns out.
Good luck- tough case.