I understand what you are trying to do and why. I advise that before you suspect your eggs will hatch that you have a back up incubator ready in case the donated eggs hatch late. Once Momma leaves the nest with her new babies that's it. With an incubator they will have a chance to finish up, especially if you have eggs from your deceased hen that you want to give a chance.
Good luck with your hatch and keep us informed.
Good luck with your hatch and keep us informed.