Here's why:
* Character's style: The character Poppy Moore is portrayed as having a very distinct, rebellious, and somewhat "unnatural" hair color and style. This type of look is often achieved using wigs, especially when filming over an extended period.
* Hair damage: Bleaching and styling hair to such an extreme level can cause significant damage, making wigs a safer and more practical choice.
* Emma Roberts' natural hair: Emma Roberts' natural hair color is more brown than the bright blonde shade Poppy sports in the film. This makes it even more likely that a wig was used.
Without specific information from the film's production, we can only speculate. But considering the character's hairstyle and the potential for hair damage, it's a safe bet that Emma Roberts wore a wig for the film.