Roberta loses interests when she goes broody the following year.
Have you got a house and run available for her when the chicks hatch? I use a rabbit hutch with a chicken wire fence with more wire over the top.
She is fine for the food and water, but when the eggs hatch you will need chick crumb, which your layers should not eat.
Grinling is right, you will need chick crumb - it is small enough for the chicks to eat and most contain anti-coccidosis medication which is why your laying hens shouldn't have access to it. Once they go onto growers (also medicated) you can't feed the remaining crumb to your hens and will need to dispose of it. the same goes for any growers left over. You will also need a shallow drinker that the chicks can't fall into and drown. If you don't have one a flat saucer with some pebbles in the bottom should do.
Your hen should stay with the chicks of her own accord for anything up to 6 weeks, maybe longer. You will know when she wants to go back - she'll make that quite obvious! However, you will need a contingency plan in case she decides to abandon the chicks and they are not yet off the heat. Have a search through the site for home made brooder boxes and have a large box on standby just in case.
Keep an eye on your hen whilst she's brooding - they often neglect to eat and drink, so if you notice that she has not touched her food you will need to carefully lift her off the eggs so that she can do so - I used to feed her pellets in a shallow dish so that I could level the top -this would easily show if she had taken any pellets. From day 18 onwards don't lift her off, she needs to stay on the eggs. Don't worry abount candling - any unviable or rotten eggs she will kick away after a couple of days.