Bathing your kitten
As posted earlier, you shouldn't have to bathe your kitten. Kitties are immaculate and very dedicated to keeping their coats clean, shinny and in place. If your kitten got into something that could potentially harm her then you would need to bathe her. If you are noticing that your kitten's coat has a very oily look to it and starts "clumping" together (like our hair if we haven't washed it in a few days- gets stringy, greasy and not nice looking) and you don't notice her grooming herself, there may be something going on with your kitty. One of my kittens have medium length hair and it always looked nasty and greasy, but this was because he was a VERY sick kitten. I fostered him and his sister who were listed as "failure to thrive" and then eventually ended up adopting them, knowing that their special needs status would make them undesirable. Poor thing was so sick he didn't have the energy to groom himself. His sister did most of his grooming, but she too was sick and her coat had it's own issues. I gave him baths occasionally and then other times I would use the waterless shampoo on him and then comb him, which he liked better. I eventually shaved him because he just couldn't keep up with his coat.
If your kitty doesn't appear to be ill, and like the previous person said they aren't the time of breed that needs baths, then you may want to consider the diet. Is your kitten getting all the proper nutrition that she needs? If you see her always scratching at her ear or chewing on her feet, it could be an allergy to the food. Flip your cat food bag over, what are the first 5 ingredients? If it's not mostly protein, chances are that she could be allergic to the grains or the food has a bunch of filler. If you want to experiment, you can switch her food for 1 month to another brand (preferably one that is no grain and with only one protein source) and see if her coat starts to look better. There are some brands that if you request it, they will send you samples to see if your cat likes it. I personally use Blue Basics or Blue Wilderness because one of my kitties is food sensitive and the other was so malnourished in the first few months of her life and they BOTH have immune system issues, they need that higher protein, plus they are really great about standing behind their products and sending out samples. If you buy a bag and it's not helping your kitty/or kitty is getting worse, they take it back and reimburse you- no matter how much of the bag is gone (granted, if there are only a few kibble pieces they may lift a brow).
If none of these seem right, you can always talk with your vet about it at your next appointment. Just make sure that she is EDPP (eating, drinking, peeing, pooping-these are the big 4 that they always want to know) and if your kitty is vomiting or loosing weight depsite eating good, you need to get into the vet right away.
Good luck with your kitty! Let us know what you find out.