Hi - I am sorry to hear this. It might be that Xmas in the care home has confused her or made her more tired/exhausted - and I say this because my father had his Xmas party yesterday and he's not been the same since! Double incontinence, very muddled, telling me he's had no breakfast or lunch today, also telling me that there's NO ONE HERE, NO ONE AT ALL, meaning that there's no carers OR residents! When I was on the phone to him TWO carers attended (I could hear them talking to him AND he replied) but he still denied that there was anyone in the premises AT ALL.
So yes, this sounds to me like the Xmas season has disrupted your MIL as it has my father - although please ask the home's manager if MIL has been tested for any infections as this can cause odd changes in behaviour.
Keep us updated!