She looks like she sorta has tabby stripes hidden on her. I have seen chocolate coloured kittens before when volunteering at the spca so i doubt she's unhealthy. The kitten I just bought two weeks ago looks very similar to yours, but she's longhaired and has bits of orange and white on her (very cool pattern, kinda looks like a diluted torbie). Not sure what breeds she has in her either. You may be able to find a DNA test you could get her to take if you really really wanted to know haha.