It wasn't until their sophomore year of high school that they learned they were cousins.
So, a fashion war is essential!.
Thankfully, this was only a brief scene and she never put it on again.
With two people gone from her immediate family, it left her distraught and incapable of continuing with life.
The dress is meant to flatter Cheryl's frame and to make her look taller than she is, as it adds the illusion of a long torso.
Cheryl blossom goes hollywood third limited series; Cheryl blossom in white dress, homage to marilyn monroe in the seven year itch; Source: hips.