I had a dc child like this and I kept him for almost 3 years and it sucked me dry......I would never do it again.....you also have to worry that she could hurt the others if she gets upset enough.....I'd be very upfront with the mom and tell her if the behaviour does not stop, then dc child will be terminated and stand firm to what you tell her.....mine was a single mom too and I constantly spoke to her and tried to help this little guy as I had come to care a great deal for him, but in the end, it was just to much and was not fair to the other children....good luck