The mother is capable of raising them, but some broodies just aren't very good moms. They get bored of their babies.You might lose some chicks if you let her try to take care of her own chicks. On the other hand, it's less work for you and it's the natural way to do it.
Like said before, just depends on the hen. Some just like the sitting aspect, some like to raise chicks (and I have two of those that steal babies to raise). Go ahead and give it a shot. You may want to put momma and babies in a small to medium cage for now though so you can watch them interact.