@Oysterwhite
Not really, Rosa has been hinted to being this despicable before, we have seen her being mentioned of going out with various men, abusing Maria, and leaving Maria alone in the past volumes. The difference this time is that we are actually seeing her interaction with Maria privately now, unlike in the previous volumes when she was in public.
Remember this is the same woman that beat her child , until she was swollen, in public, and left Maria alone in the rain, in the garden were Beatrice found her. So her acting like this to Maria in private is not that far fetched,and just like rosa herself said when she was being tortured by Beatrice in the golden land, she is a very bad mother.