A hen cannot sit on eggs to keep them warm, and also walk around teaching chicks to eat, at the same time. It is just not possible.
If you put food and water right next to the hen, she might stay on the nest until the last ones hatch, and the first ones will be able to eat and drink right there. That's "maybe" she will stay on the nest, not a certainty. (Of course it is fine if she still comes off to poop, but if she is off all day those eggs will be in big trouble.)
If you set up a brooder, you can take the first chick away and start raising it in the brooder. Take each chick as soon as you see it has hatched, until the last one hatches. Then return all chicks to the hen. Possible problems: the hen might come off the nest anyway when the first chick hatches, or she might refuse to take the chicks back after the rest hatch.
If you set up an incubator, you can watch for the hen to get off the nest with the first chick, then move the remaining eggs to the incubator. When each chick hatches, let it have long enough to be steady on its legs, then give it back to the hen. Of course, she might not accept the chicks back.
Every option I can think of has some uncertainty, and I do not know which is easier or better in your situation, or which is more likely to work.
For future, try not to let eggs get added to the clutch after she starts setting. You can mark the eggs, then check each day to remove any new (unmarked) ones. Or you can separate the setting hen from the others, so the other hens cannot lay eggs in her nest.