What is the ruling on a woman in the state of Ihram letting down her hair?

Removing head hair by any means is among the prohibitions of Ihrām. It is forbidden to comb or brush hair if it leads to its shedding. If the hair does not shed by combing, jurists have differed on three opinions: permissibility, citing the hadīth of Aisha (may Allah be pleased with her); prohibition, citing a weak hadīth; and dislike (karāhah), which is the opinion of the Shāfiʿīs and Hanbalīs, because it is more likely to expose hair to shedding. This last opinion is the most equitable. If a muḥrim finds hair in his comb and does not know whether it fell due to the comb or was already loose, no fidyah is due from him, because the default is non-obligation based on doubt.