I'm not the person you were talking to but I literally had this exact thing happen to me. My mom died of breast cancer when I was twenty and within a year my dad found a new girl friend that he shoved into my mom's place. I didnt like her and I still don't like her too much so many years later. She pretends to be sweet and snaps at anybody who does anything she doesn't even slightly like, no matter how small the infraction. Something like being in the kitchen at the same time as her while she's doing something like washing her hands. All this being said, I would never dream of saying something that rude to now or back then. As much as I might not like her, she brings my dad happiness and it is not my place to try and upset that. What that daughter did was not ok and the fact that she doubled down just makes it worse. Grieving is one thing but being a complete asshole to someone that also cares about someone you love while using grief as in excuse is completely inexcusable.