Check out where she is going. If you can put a kennel around her for a little bit, rig something up. She will get eaten if she sits on her nest. Also, dakinsmimi is right. Guineas are not so great with mothering. Quote from Frits Farm site, "The nest is extremely hard to find, so, when this happens, there is a really good chance you might just lose your hen to a predator. Try to find her by searching along the fence rows and in high grasses. Her mate might be seen guarding her during the day, but will usually go home to roost at night when she needs his protection the most.
You might want to consider setting up a dog kennel in your barn or henhouse, and moving her nest and all, into that kennel. If she is determined, she will safely hatch those eggs, and take care of her keets. If you allow her to stay in the open, and she does hatch her eggs, most likely they wont last long. Guineas are not the best mothers when outdoors, sometimes taking their keets out into wet grass or leaving them in the rain, which is the keets worst enemy. In all the years I have raised guineas, I have yet to have a guinea hatch a clutch and bring any keets home alive on her own. Either a predator or the wet grass gets to them first. If you want to let her stay outdoors on the nest, at least try to enclose an area around her with some temporary fencing so she will get some protection from predators."
