Attorneys general from California, Colorado, Kentucky and New Jersey are seeking extensive financial damages plus changes to how the company operates Facebook and Instagram.
Parents interviewed about the verdict said they view the decision as a step toward stronger protections for children.
The woman - identified in court as KGM - is the key plaintiff in the case, which alleges she began using social media as young as age 6 and became dependent on the apps.
Adam Mosseri, the head of Meta's Instagram, testified Wednesday during a landmark social media trial that he disagrees with the idea that people can be clinically addicted to social media platforms.
The world's biggest social media companies face several landmark trials this year that seek to hold them responsible for harms to children who use their platforms.
When her so-called mentor suggested she sell her car and all her physical belongings at a pawn shop to try and 'unfreeze' her account, Dawn Furseth realized she had been scammed.