The only statement I read was on People's website and they had said she was in Arizona on her doctor's orders.
Personally, I think Katherine is a little too up in age to care for 2 teens and a tween and think that she's going to raise them all JW-ish. I don't think taking custody has anything to do with the JWs, but has more to do with her abilities to care for them, seeing as she possibly has some health issues to deal with. They'd be better off with their aunts, uncles, and cousins at this point.