She definitely sounds too young and unstable to be taking care of a kid. Have you been in contact with child welfare yet? How's it all going?
Btw... is 17 underage where you live? It certainly isn't in my country, but some of the other replies make it sound less than kosher. What's the deal?
I sincerely hope that everything works out for you and for Shaun.
All the best,
Kal