What is your advice to Muslim girls and women who observe prayer and the lawful hijab during Ramadan, then abandon prayer or wear a fashionable hijab or remove the hijab completely after it ends?

Allah has made the hijab obligatory for Muslim women, and it is not tied to a specific time or place. A woman's presence in a situation where non-mahram men can see her necessitates veiling and hijab to protect herself. It is strange for a woman to pray and yet not adhere to the hijab, for the One who ordained prayer is the One who ordained the hijab. True prayer helps its practitioner avoid what displeases Allah: "Indeed, prayer prohibits immorality and wrongdoing." There is no reason to differentiate between one month and another in adhering to hijab and prayer, for the Lord of Ramadan is also the Lord of other months, and the believer is commanded to worship Allah throughout all ages: "And worship your Lord until there comes to you the certainty (death)."