My first broody hen just hatched a chick which died at 5 days old. Then she hijacked some more eggs and started sitting again, but quit after 5 days.
I'm not sure if you can't make a hen go broody, she just decides on her own...whether there are eggs in a nest or not (fertile or non fertile)
When they do go broody they will stay on eggs with this glazed look in her eyes. She'll get mad if you take her off the nest or even if you try to touch her. Mine growled, I've heard that others' peck at them. Mine was very sweet and let me do what I wanted, but she did let me know, verbally, that it bothered her. If you take her off the nest, she'll run right back onto it. Her body will also look round and flat while she's sitting (that's what mine did anyway)
Mine started laying at 16 weeks old and went broody at 19 weeks old. But so far, she's the only one that has gone broody and now they are all 24 weeks.
You really can't miss that a chicken is brooding...it's very obvious. Maybe if your wife sees another little chick she'll change her mind?