WHY DO PEOPLE THINK THEY ARE BETTER THAN OTHERS?

I USED TO BE FRIENDS WITH THIS GIRL. SHE ALWAYS THOUGHT SHE WAS BETTER THAN ME. SHE WOULD ALWAYS FLIRT WITH ALL THE GUYS MAKE ME LOOK BAD AND ALWAYS SAID SHE WAS FAT EVEN THOUGH SHE WAS LIKE A SIZE 1 IN JEANS. I WAS ALWAYS THE UGLY ONE TO HER. NOW THAT YEARS PASSED BY SHE THINKS SHE HAS A PERFECT LIFE. I HAD A BABY AT 16 AND IM 19 YRS NOW AND SHE JUST HAD A BBY IN OCT. AND SAYS SHE LOVS HER LIFE AND TRIES TO SHOW OFF..IM HAPPY WITH MINE ALL THE WAY BUT DO YOU THINK SHE STILL WANTS TO BE AT THE TOP EVEN THOUGH I TOLD HER I CANT BE HER FRIEND. P.S SHE ALWAYS HAD BFS IN HIGH SCHOOL AND WHEN I LIKED A GUY SHE SAID I WAS A BACKSTABBER CUZ I TOOK HIM AWAY. SHE ALREADY HAD A BF AND IT WASNT HIM.?