Is it obligatory for a woman to remove henna covered with a piece of cloth from her head for ablution for Fajr prayer, or is it permissible to wipe over it?

If henna prevents water from reaching the hair, it must be removed for ablution (wudu'), and ablution is not valid with it present, because Allah Almighty says: "and wipe over your heads," and the letter ba (ب) denotes adhesion. So, if the henna forms a barrier, adhesion is not achieved. However, if the henna does not prevent water from reaching the hair, then there is no impediment to wiping over it, with the reminder that wiping over a cloth covering the henna is not sufficient.