Played by julianna margulies what er character was originally supposed to commit suicide and die in the first episode but instead simply

The character you're thinking of is "Carrie Bradshaw" from the HBO series "Sex and the City".

Originally, the plan was for Carrie to jump from a bridge in the first episode and for the show to be a reflection of her friends processing her death. However, Sarah Jessica Parker's performance convinced the creators to change course and instead have Carrie survive the attempt and the series focus on her life going forward.