Not everyone who studies dark magic wants to become the Dark Lord. Why does nobody believe me when I say that? Does she think she doesn't have enough Potions essays to write, or that magical history is too easy to memorize? Why would she go looking for this kind of trouble?
Rosette Black is very troubled. She simply likes dark magic. Other than that, she's always been a law-abiding, well-behaved witch. But ever since she started studying at Hogwarts, it seems everyone has treated her like a future Dark Lord.
Rosette has no desire to become the Dark Lord! Being the Dark Lord means getting disfigured! You don't just get disfigured, you lose IQ points too!
She just wants to quietly be a witch devoted to her studies and pet cats in her spare time. She definitely doesn't want to take on such a thankless job.