Unfortunately, Lakelight has indicated that her mother has always behaved in an abusive manner. If it were as "simple" as Alzheimer's, etc., I imagine it would be the best news imaginable. At least, those organic causes of instability can be managed and explained.
When an individual is abusive, there is no reasonable explanation (part of the cycle, be dammed) for deliberately inflicting damage upon other human beings, often, with malice aforethought - the abusers know it's unacceptable behavior, else they wouldn't go to such great lengths to explain away their behaviors as something that the victims caused and, ultimately, deserved.