By Emma Rowbottom A woman has told how she got ‘petty revenge’ after her engagement party was hi-jacked by her ‘scheming’ half-sister. After admitting the half-siblings, who were both 24 years old, never really got along, she revealed how her father had left her mother for her half-sister’s mother, with both girls born in the same month, only 20 days apart. She also told how the relationship with her half-sister, Heather, had ‘always been weird’ saying: “She has always tried to one-up me, even though we both have a similar economic background.” After she announced her engagement to her fiancé …