Unfortunately I'm familiar with this. Had my big girl eating f/t for 7 months or so, and now that she's developing her follicles she's only taking live, not even pre-killed. Before she laid last year she would also only eat live. She was so voracious after laying her eggs she went onto f/t no problem.
My big pinstripe girl was also on f/t up until about 1.5 months ago. She started refusing and I haven't bothered trying to feed her live as I believe she is going to lay her eggs in a week.