She has become vindictive, controlling and generally nasty, then minutes later or the next day she appears as though nothing has happened. Days later she again will upcast and verbally get her nasty points across once again starting the argument. She won’t spend much on her clothing yet has more than enough money to do this. Mam has also taken it upon herself to be nasty about my son and his fiancé calling her “She” if I allow her to get away with it.
She may not have the capacity to remember your dil to be’s Name.
I had a neighbour who after a stroke could not differentiate between males and female. Her brain was broken.
Yet she could still play bridge for several more years.
If there is no infection, then it is your Mom's Alzheimer's/Dementia [as per your profile] that is causing this behavior. Have a chat with Mom's primary doctor to see if there is something he/she can prescribe to help.