Hi, how is the kitten today? Good she is eating and gaining well at least. How does the congestion manifest? Is there sneezing or a rattling noise? It could be a number of things, an allergy, or a uri, or something and nothing that passes quickly, etc. either way if you are in the position to do so and it is unchanged since you posted this might be a good idea to get a vet appt and get a more informed opinion.