Can a hen can turn into a rooster?

No, but we can give you some background information and share the crazy way that rumor may have gotten started!

It IS true that, if your hen has had some damage to her reproductive system (such as an infection in her ovaries), she might begin to look like a rooster on the outside---and act like one---due to a hormone imbalance! Such a hen wouldn't lay eggs, and may even begin to crow. At her molt, she may grow in the same plumage roosters have in her breed. If her infection or condition then cleared up, she might begin laying anew, stop crowing... and at her next molt she would grow in henny feathers again.

She would still be a female chicken the whole time, just like human women are still females even if they have hormone imbalances or are infertile for various reasons.

There was a famous case in 1474 when this apparent "sex switching" occurred with a chicken. It was the case of the Rooster of Basel and she was solemnly burned at the stake for "the heinous and unnatural crime of laying an egg." What caused this "rooster" to lay eggs was not a sex change, though. It's likely that the poor hen simply had a hormone imbalance or an infection which in her ovaries which cleared up, so she began laying again, while she was still feathered as a rooster. For this heretical outrage, the poor girl was taken to court by the clergy, found guilty and burned as a witch. Afterwards, the executioner is said to have cut her open and removed three more eggs from her body.

Don't hate me because I'm beautiful!

There was also the case of a buff orpington in 1922 in Britain, and a case in 1927 of the "Rooster of Madison" here in the United States. Luckily, the last two hens were merely regarded as curiosities and appear to have led normal, chickeny lives rather than being put to death by superstitious religious fanatics.