Sweet hen turning aggressive

I have a 12 week old pullet as a family pet who's always been the sweetest thing. She loved cuddles, would follow people everywhere, and fall asleep in my lap. She still does all of that, but recently she's started to have moments where she'd turn very aggressive. The majority of the time when I pick her up, she'd happily step onto my hand. But sometimes, she'd turn around and either peck or bite me pretty hard. Today, when I turned my back on her, she raised her hackle feathers and literally attacked the back of my ankle with her beak and claws. Then, of course, the next time I'm around her she'll be back to her old sweet self.

Does anyone know what's happened with my hen? I've raised her from an egg and giving up on her isn't really an option. I've been telling her "NO" with a stern voice when she's acting up, but it doesn't seem to be working. Is she going through some kind of teenage rebellious phase or what? I've even started considering that she's a rooster, even though her hackle/saddle feathers, comb/wattles, and size all indicate female. Is she possibly considering me another hen and trying to get above me in pecking order?

any advice is appreciated.

If you want to post a picture we can tell you what we think her gender is, just in case she is a rooster. Sorry you're experiencing this!

She does look like a pullet; I'm not sure what's going on. If she attacks you again try pinning her down and holding her there for a minute, then letting her go. Maybe she's treating you like another chicken in the pecking order (that's usually what causes rooster attacks) and if that's the case this will assert your dominance and she might stop. Otherwise I'm not sure what else you can do; maybe someone else will have some ideas.

Does she look like shes trying to size you up before she 'strikes' or is it really just coming clear out of know where?

And is she near the top of your coops peaking order? Because if the answer is yes, then I'd have to agree with Pyxis. It sounds like she's trying to 'put you in your place' which would also be why she doesn't feel the need to always be aggressive. She's not scared of you just looking to figure out how you fit into 'the flock'.

Putting her in a 'submissive squat' should help if that's the case. Also pushing her back from treats and making sure you 'having some first' might help her see you as higher up the food chain (no pun intended).

(I've never tried this myself but you can also trying giving her a poke with your fingers like another hen might with their beak...?)

Rosie is not part of a flock. She started out as a classroom project and I was unfortunately not able to home more than her. She's always been aggressive to other birds and very sweet to humans since she pretty much "imprinted" on a person. I suppose it's very possible her chicken wild side is showing itself during puberty (her voice just changed) and is now trying to dominate me. Regardless, I'll try your suggestions. Thanks to you both.

Update:

Her behavior is now concentrated towards my feet. She's no longer pecking at my hand when I pick her up, and shed happily settle down on my hand. Could she be seeing my feet as something different from me?

A lot of roosters attack feet because it's what they can reach, and she could be doing the same thing. If she imprinted on people, she definitely thinks you're a flock mate and she's probably trying to see where you and she fit in the pecking order now that she's old enough that she doesn't regard you as her mother any more. Try asserting your dominance over her and see if she stops with the attacking behavior.

Does she have any real flock mates, or is she your only bird? You might try getting her a real flock mate and see if that helps, too. Having healthy interactions with another bird might improve her mental state.

My Phoenix does this, sweet one day and feathers up coming at me the next. The last time I poked her "like a beak" or another chicken and it worked. She still pecks my feet but No other signs of dominance. about every other day we go through this. Sweet girl but right now she's ignoring me cause she didn't like the tap I gave her earlier.

Unfortunately, i live in an urban/suburban area. The only way for me to get any chickens is to order a huge batch of chicks online, which wouldn't be very possible with my tiny yard and close neighbors. I think what you said is definitely the most likely explanation. If i assert dominance, will my chicken still "like' me?