Have you tried leaving one in overnight? I'm assume he said live mice right? You've tried both live, prekilled and F/T or only prekill?

In winter they tend to go off feed, although this is more common with males, and ovulating females, others may go off as well.

Has she lost too much weight? Maybe the guy tried to breed her already and it set her off feed (not healthy, but you'd be amazed what people will do).