By Tom Nouvian CASSIS, France (AP) — In the moment when her world shattered three years ago, Stephanie Mistre found her 15-year-old daughter, Marie, lifeless in the bedroom where she died by suicide. “I went from light to darkness in a fraction of a second,” Mistre said, describing the day in September 2021 that marked the start of her fight against TikTok, the Chinese-owned video app she blames for pushing her daughter toward despair. ___ EDITOR’S NOTE — This story includes discussion of suicide. If you or someone you know needs help, the national suicide and crisis lifeline in the U.S. is available by calling or texting 988. There is also an online chat at 988lifeline.org. Helplines outside the U.S. can be found at www.iasp.info/suicidalthoughts. ___ Delving into her daughter’s…