Might be playing devil's advocate again but sometimes people even "friends" just feel that certain family issues aren't any of their business. You know, not their place to disclose someone else's secrets or problems. Suppose her friend had told you, you may have very well been one of those mother's who'd flat out call the friend a liar in disbelief that your child would do such a thing to herself or her unborn child. It happens like that often.
You've stepped in and have taken your grandson away from a bad situation and that shows amazing strength on your part. You're a terrific grandmother but try not to be so hard on the friend. Yes, she "enabled" your daughter but we're guilty of enabling the addicts in our lives as well. We have to tell ourselves not to beat ourselves up about it because we care about them and we're ignorant as to how to help otherwise. It takes education to know how to properly react to these kinds of situations. Her friend(s) are only human. Of course, it is your perrogative as to how to best handle those kinds of phone calls from here on out and certainly your first priority to protect your grandson from overexposure.