Male is XY and female is XX. If a female pollinates itself there is no Y present therefore it is not possible to make XY, only XX. Some of those females have an ultra high chance of being hermie though. This process is similar to the one that they use to make feminized seeds. The only difference is that breeders collect the pollen from a hermie plant and not the seeds. They then take the female pollen and pollenate another female plant with it. They do this multiple times in order to stabalize the genetics and reduce the possibility of more hermies. Once the hermie chance is as low as it's going to get they sell the seeds as femanized.