I'm not sure it was exactly the prospect of losing her children, I think it was what came with that - how she would be seen as a neglectful mother, and also losing the kids benefits, her house, perhaps even the scandal affecting her job as a carer, basically undermining everything that was holding her in the position she was in where she was in control.
It sounds like she blamed Bee as well and I don't see her as being particularly fond of Bee. I can't imagine my daughter telling me over a text, under the same roof, of such a traumatic experience and sending texts back! Not actually talking to her face to face and holding her. She doesn't have the nurturing, empathic instinct I don't think, it's ALL about Sarah.
As the prosecutor said “All parental love and responsibility had gone - if it had ever existed."