Who has legal custody of your grand daughter? Where was your dtr. all of this time and why is she returning now. You are right to be concerned about your grand daughter's behavior and well-being as your dtr.abadoned her at birth and has re-emerged into her life. A young child doesn't have the coping skills to deal with such unsettling life changes. You need to stand up for this little girl.
I agree with Cleveland Mom 100%. If your daughter doesn't have custody of your granddaughter, I would work out visitation for her. That way you can prepare your grandaughter for the visit versus your daughter just walking in anytime she feels like it and taking your grandaughter. Put your foot down.
Grandma, If you have legal custody of your granddtr. and mom up and took her from you without your consent she has violated the legal custody agreement set up by the court. You should contact authorities, the police or child protective services.