Answer
As of my knowledge cutoff in September 2021, Carmella has won the WWE Women's Tag Team Championship once alongside her partner, Bayley. They captured the titles by defeating The IIconics (Peyton Royce and Billie Kay) on the July 22, 2019, episode of Raw. However, please note that there may have been subsequent title changes beyond this date, so it's best to check up-to-date sources for the latest information.