Tensei Koushaku Reijou Funtouki: Watashi, Rippa ni Zamaa sarete Misemasu!

One day, the Marquess's daughter Julianne suddenly regained the memories of her previous life and reflected on her behavior up to this point. A life of luxury, bullying her siblings and stalking her fiancé... A horrible personality and overweight appearance, devoted only to wrongdoings that belonged to the villainess of the novel she read in her past life. In any case if it is a "serves you right" fate from now on, then it will be after I get a beautiful body and soul! She, who thought this, started a diet together with showing a wholehearted devotion to her family—?!

(Source: AlphaPolis, translated)