Is a mother sinful for not immediately forcing her recently adult daughter to wear the hijab, preferring gentleness and waiting for the daughter's promise to commit to it at the beginning of Ramadan, while the father insists she wears it now?

The hijab becomes obligatory for a girl as soon as she reaches puberty. Parents must immediately compel their daughter to wear the hijab upon puberty, because abandoning the hijab is considered tabarruj (improper display of adornment), and tabarruj is forbidden.

Allah Almighty says: "And do not display yourselves as [was] the display of the former times of ignorance." (Al-Ahzab: 33)

And Allah Almighty says: "And not expose their adornment except that which [necessarily] appears thereof." (An-Nur: 31)

The father must compel his children to obey [Allah] and keep them away from sins, even if by force.

The Prophet, peace and blessings be upon him, said: "Indeed, all of you are guardians, and all of you are responsible for your subjects. The ruler who is over the people is a guardian and is responsible for his subjects. A man is a guardian over the people of his household and is responsible for them..." (Narrated by Al-Bukhari and Muslim).

Allah Almighty says: "O you who have believed, protect yourselves and your families from a Fire." (At-Tahrim: 6)

And the mother should be a helper to her husband in raising their children according to the rituals of religion.