Double Edged Villainess

She was only lazing around during her holiday break when suddenly, she wakes up in another body...? "Who's body is this? Where am I?" She learns sooner than later that she's now inside the morbid fantasy book she read during her childhood, "Princess of the Guillotine", which depicted the evil deeds of the villainous princess against the heroine. What's worse is that she transmigrated into the Princess's body a day after she killed one of the heirs of the throne for her manipulative half-brother. Just how would she survive now?