I have had some success with setting chicks under broody hens. And also some fatalities. If you want to give her eggs, you should make sure she is committed to hatching them. I wouldn't take her off her nest. She knows when to get off to eat or poop, even though it may seem like she doesn't. Sometimes they are only off for a short time. You can set food and water near her so she doesn't have to get up to eat. 7 or 8 eggs is a good number.
My Buff Orpington has hatched eggs that I placed under her, and was a very good mother to them. I waited til she had been on her nest, un-interrupted, for about 10 days, then waited for her to get off the nest. When she did, I went in and traded out her wooden eggs for the fertilized eggs. I could hardly leave her alone when I saw those little pips! I would much rather raise chicks by giving them to a hen, and eggs is the easiest way to do it. The Mama hen does all the feeding, raising, teaching, warming and protecting, and it SO cute to watch.
I've also had some success with giving a Broody hen chicks, but you have to be more careful. I've found that you have to be very careful. In my experience, it is best to sneak the chicks, (day old's are best, otherwise they have difficulty bonding with the hen.) in at night, without her seeing you. I have always snuck up to her very quietly, under the cover of darkness, reached around the side of the box and quickly slipped a chick or two under her . Then I wait a few hours and slip a couple more under her. If you add them all at once, it seems to startle her off the nest. It's not natural for them to all "hatch" at once.
After you give her the chicks, you have to REALLY watch her. If she shows ANY aggression toward them, they need to be removed quickly. They will either die from being hen-pecked, or from being too cold, and it doesn't take long in either case. Have a broode set up that you can move them to quickly if needed. If you are trying to add chicks to a hen for the first time, I'd recommend giving her only 3-4 to see how she takes to being a Mama, then maybe give her a couple more next time. And remember, Nature knows best, and as hard as it is, if you want a successful transition, be it eggs or chicks, you have to let them be. (Unless the hen is being aggressive, of course.)
Let us know what you do and how it goes!
