There may not be anything "wrong." She is not too young, but she may be too inexperienced to follow her instincts and set on the eggs. Some guinea hens never go broody because the instinct has been somewhat bred out of them with domestication. Even if a hen does go broody, she may not complete the task and may get off of the nest before the eggs have hatched. Sometimes it takes a second try at incubating to complete it. Guineas don't need a nesting box or a typical nest to lay in. Any area that is secluded and private will usually work. It helps to have a place with something overhead like beneath a shelf or behind a slanted board. You could crack open one of the eggs to find out if the egg has been fertilized.
