When I had one of my female Bettas in with my Mollies (one male Black, one female Marble, and one female Silver), the Silver Molly picked on her mercilessly, the Marble Molly pretended she didn't exist (except when the Betta flared at her to get her to go away), and the Black Molly tried to mate with her until she flared and postured him into going away. I found the female Betta after only a couple hours in a corner with the Silver Molly nipping at her. The female Betta was laying on the marbles and had given up trying to get away from the Molly. It was JUST that Silver Molly that picked on her, and, even though that particular Molly is quite dead now, I don't think I'll ever put my Bettas in with my Mollies again.