I had a female betta that was in a tank with some platty's and some female guppies. She was the best female betta I had ever had. She ended up in the same tank with an aggressive male silver molly ( it was only going to be for 10 min tops ) He actaully attacked and killed my female betta
Also it is a bad idea to mix female betta's. They will fight ( even though you see them mixed in pet stores all the time )
back to topic though your female betta was just trying to mate with the male guppies. There is a lot of fin ripping that goes on in their mateing. Though some female betta's are just plain evil sometimes
