Many Christian women do that, like nuns, some brethrens and Hamish, etc.
Nadiya seems to be a very stong woman, and her husband a really kind and supportive man- who was happy to take care of the family and give her a chance to prove herself and shine- which is what counts, surely.
I am pretty sure Nadiya chooses to wear a head covering, because that is what SHE wants to do. Very condescending, even if not intentionally, to claim otherwise.
It's possible that in her own home she doesn't wear the scarf. I was teaching a class of mature students. When we broke for coffee, the men all went out and the women stayed chatting with me. Our Iranian student took off her scarf and revealed a very short blond hairdo. She was also wearing jeans and trainers. He mother used to send her pretty scarves from home and she always looked good.
When I was in Bangladesh the women I was with didn't cover their hair. In fact they positively looked down on those that did. One told me that it was just a pointless throwback to the days when arabs were in the desert. Bangladesh was never a desert area.
I don't watch GBBO but it doesn't make me feel sad to see someone wearing a hijab - I assume they do so from personal choice. I personally don't like pierced cheeks, lips or rings through noses (studs are ok) and think they are quite disfiguring, but the owners of the piercings obviously feel differently and it's entirely their choice.
I was very glad Nadiya won, she was a worthy winner and her range of facial expressions endeared her to many of us. BTW she has a very handsome husband, he looks as good as some of her edible creations!
My only thoughts about the hijab in the kitchen, is my god it must be hot under that lot, she has a few years yet before she goes through the menopause, but she might find it a bit uncomfortable at that stage, although I'm assuming that she wouldn't wear it in her own home?
Quite frankly given the current climate of negativity towards immigrants, I don't think Nadiya could have picked a more perfect time to win. Having watched her every week on the show, maybe some people will have a hard think about their perceptions.