I'm not sure what the child protection procedures are in San Francisco, but I used to work in a related field in another U.S. state and "taken into care" might mean a different thing in the UK than it does there.
The fact that this little girl has been "taken into care" most likely means that the Department of Children and Families has assumed temporary custody of her and placed her in another home - possibly a foster family but very likely her own relatives, which is always the first option if at all possible - until a court hearing at which a family court judge will determine whether she should be returned to her mother's care, and if so whether that will require support from DCF (home visits, parenting classes, whatever).
I think it's a reasonable response, and hopefully was done as sensitively as possible for the poor little girl. Her mother needs to know that this was not acceptable.