Hi there, you are through to Dr. Jake. Im a UK based vet. Im sorry to hear of your concern with your kitten.
It sounds likely that she is the runt of the litter, in the wild/ nature they often dont make it and mum can sometimes abandon them if they think they will be using up resources and will concentrate on the healthier ones.
You will likely need to start bottle feeding this kitten with kitten formula you can purchase online or from a pet store if you havent already done so.
The closed eye could be a sign of an infection which it affecting the kittens system and making it not want to suckle.
There is always a possibility that there is something wrong with the kitten that had happened through development inside the womb. there can be a range of organ abnormalities and malformations including organs such as the heart, liver, stomach intestines which are difficult to detect at such a young age and small size.
I would recommend an appointment with an emergency vets today if your regular practice isnt open from consults for a full examination to see if they can detect any underlying conditions. they will be able to provide appropriate treatment such as eye drops an antibiotics if the eye is infected and may also be able to provide you with some rearing formula.
For all the kittens i would recommend weighing them with kitchen and bathroom scales on a daily basis to make sure they continue to gain weight as a sign of weight loss would be a que for you to take them to the vets. Make sure during the suckling period that mum has plenty of food as producing milk takes a lot of energy and she can loose weight rapidly if she isnt provided with an adequate diet.
I hope all this information helps