RIR hens seldom go broody. Occasionally you hear about one that does but I consider that to be an exception. I would not count on it
but would get an incubator. I would not expect a pullet that has just started laying to go broody for a long time if it ever does.
It is a fairly complicated process for a hen or pullet to put an egg together. It is pretty common for them to get something wrong when they are first starting out. That's not just the stuff you see but stuff you cannot see that still has to be correct for the egg to hatch. A lot of pullets do get it right from the start but many don't.
There is another issue. When they first start laying the eggs are often pretty small compared to how large they will be. There is not enough room in the egg or enough egg material to grow a strong healthy chick. As they lay the eggs tend to get bigger.
I've hatched some small pullet eggs. Some of them do fine. But my hatch rate with them is often not great. If a chick hatches it usually lives and does well. But if I have a chick die pretty young it almost always hatched out of a small pullet egg.
My suggestion is to wait until that pullet has been laying a month before you hatch any of her eggs. I think you will see a better hatch rate and the chick's survivability will be better.