That is one of the saddest personal accounts of witnessing the ravages of child abuse I have ever read. You were NOT being cruel. I have many feelings after reading this and none of them are appropriate to voice in a public forum or while I'm still feeling them so acutely.
Thank you for caring for this little angel and for being firm and strong with this "mother". I don't care that she's 16. There are plenty of 16 year olds with a far better understanding of compassion, love, and motherhood. I know. I've met them. I know the mother's situation growing up may not have been ideal and that may contribute to her "inability" to provide the protection and care her daughter needed against this man, but in my opinion, that is STILL not an excuse.