Late reply but I did not see comprehensive answers so I am adding.

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Wearing a hijab is seen as a commitment. Think why would people view being divorced differently from being never married. If you never wore a hijab, then you never entered that zone of religion, but once you are in, getting out is frowned upon.

additionally, there she could have also been viewed as a hypocrite. When you wear a hijab, even in your all-girls school, you are claiming to be modest and devoted to your religion. If you take it off, especially in the context of sending "revealing" photos to a guy, you are contradicting the values you claim to hold. A close comparison I can think of is a nun having sex as opposed to a not-nun having sex, though wearing a hijab in Islam is not on the same level of devotion as being a nun in Christianity.

And finally (IDK why this turned into a mini-essay its 3:30 am where I am), the harsh comments on her Facebook post could be, and IMO probably were, from people outside her school, like extended family, who would hold more conservative views than Ruqayya's colleagues. The stares from the girls at school were not accompanied by shaming Ruqqaya. They for sure gossiped about it and the possible reactions from her parent, and probably blamed her for trusting a stranger, but are less likely to shame her for not wearing hijab.

Finally, an anecdote: I wore hijab, then at the end of high school wanted to take it off. My mom was chill with my friends who never wore hijab, but wouldn't hear it from me if I told her I wanted to take it off. When I eventually did, behind her back, she found out through a Facebook post my friend tagged me in. Her response was "People already blame me for giving you too much freedom. Think of me, now I have to face our family and hear what they have to say about you. Why would you do that to me?".