I've only had a situation like that once, so I don't know if this would work for any other pair. I just removed the male and left the female alone in the tank for a week or so. When I added my chosen male back in, she was much less aggressive towards him. I think she just had to be lonely for a little while to accept someone new. It may be that going immediately from her mate to a new male, she sees him as an interloper to be chased away.