She will raise them but guinea mommas are known for being bad parents. Not because they abuse the keets but simply because they are uncareful and always end up kicking, sitting, or stepping on the babies. The babies eventually realize they must avoid the legs though I have lost several keets getting squished to death underneath momma during bed time. What breed of chickens are they? Chicken babies are typically larger and more hardy then guinea keets so she should do fine with them.
Those breeds are quite large. You could compare the size of the guinea egg with an Orpington or barred rock and you will know the babies are going to be big. Guinea keets are really small during their first week but grow faster than chicks, that's the benefit of them they'll leave the brooder before chicks of the same age will.
The Guinea flew off her next for food Friday night (chicken eggs to hatch over the weekend). I ran down and pulled out the 4 chicken eggs as they were peeping and put them in the incubator! They all hatched. If the Guinea eggs are fertile, they should hatch next weekend.