Males take longer to feather. I have a oegb mixed with austrolorp and 2 out of 3 are full feathered at 6 weeks and one is not. That one already had a comb and waddles very red. If you look it up males may take longer to develop. Also yours had some thicker legs. Hope this helps.
It could be a pullet, just slower feathering. Fast feathering is supposed to be a positive trait for egg production, so if you are planning on a breeding group, have her out of it.
Otherwise, it shouldn't matter.
Vent sexing is only 90% accurate, so says the hatcheries CYA.
BUT if she's a sexlink she could just be feathering slower.
All birds are individuals, even when same age and/or same breed, you'll see other differences as things go along.