Young mallards like your girl are very curious but also ignorant, they are still learning what to do with the eggs and might try to brood, but being so young and since it's so cold this time of year they are more likely to abandon the nest, but don't worry she will probably lay again in spring and possibly a more successful hatch will come too.
has she been courting lately? This is usually the time that the females make there choice and pick their mates. If she is courting that could also be a distraction from the eggs so she gave up on them to start a new family that will come in spring
Best of luck hope.
