Now how will a spoiled villainess from medieval times survive in a world of advanced technology where elementary school students are expected to do multiplication in their heads without a calculator?
It's likely she actually can. Nobles and merchant classes most likely learned advanced math (for the time) which would have included at least long division. And the former would have benefitted from one-on-one tutelage. The exact details of their knowledge is not known, but today's elementary math is age old.
She's also not spoiled. Royalty often had little time in youth for anything but education in various topics, and her story and comments matches that. And they arguably had a higher standard of education than today's youths due to privileged, tailored education. It led many of them to be expansive seekers of knowledge in their adult life. I suspect whatever she doesn't know, she will rapidly and rapaciously find out and educate herself about it.
It's interesting...our mc benefits from the world of caricatured people forced to act out a role in playing out her fantasies. I wonder how a villainess who knows what she wants in life and is willing to do whatever it takes to get it will fare in the dog-eat-dog real world where anything goes.