It is not at all unusual for 'cristatus' males to attack or kill females after the fry have gotten some size on them. It's happened a number of times to me. As Red Devil says, the male wants to 'get it on' & the female is having a headache. She probably is also still in fry defense mode which wouldn't help matters. Having some non-territorial target fish helps ( in a large enough tank) I often use rainbowfish, they are 'smart' enough to run if chased & aren't major fry predators.