You're best not to incubate any of her eggs until she's been laying for a while. Pullets take a while to settle into a regular laying pattern and until this one does you'll probably get tiny eggs with no yolk, huge double yolkers, inconsistent shell thicknesses and various funny shaped eggs, none of which will incubate and/or hatch very well. Once she's laying steadily, maybe in a month or two, you'll be good to go.
She might well go broody, I think Cochins are quite a broody breed. But if you want to hatch at specific times, get an incubator. That way you can do it to your schedule and not to hers. You also get to hand rear the chicks, which will hopefully make them tamer as adult birds. That can be either a good thing or a bad thing, depending on what you want from your birds. Sometimes I get a bit annoyed at being mobbed and followed around by a dozen birds every time I step out of my door!