Even if you don't have fertilised eggs to put under her, you can still get your broody to raise chicks if you feel like increasing your flock.
I have successfully bought day old chicks from a local breeder and put them under a broody hen, and she has accepted them and raised them to adulthood without any problem at all. You need to leave her being broody for two to three weeks, with a couple of fake (or real) eggs under her (three weeks is the normal length of time that eggs take to hatch). It makes certain that she is really broody, and more likely to accept the chicks when you introduce them. When you are ready, place the chicks in a box near to the nest so that she can hear them cheeping for an hour or two. Then carefully place one chick underneath your broody, and see what happens. If she accepts it and tucks it under her then you can add the others one at a time.
Although my broody always accepted the chicks I gave her, you have to be prepared for the eventuality that she just might reject the chicks. If this does happen then you would have to have a brooder (heat lamp etc) and enough space to be able to raise the chicks yourself for at least a couple of months until they are old enought to be integrated with the rest of the flock.
