Although the lie could also have been a response to years of bullying; she may have been afraid that Ron and/or Harry would actively bully her/ostracize her if she didn't take the fall for it. She may have thought that their daring rescue was more to save their own arses than out of any concern for her. She was probably expecting them to be like other bullies and make her life even more miserable than usual if she didn't take the blame. And so them deciding to let her be their friend quite astonished and delighted her. And she could have easily taken a submissive role in the friendship and just gone along with whatever the boys wanted, but she stood up for what she thought was right, in her mind risking losing her new friends to tell them off for their recklessness, etc. Which would have made that first time Ron and Hermione weren't talking to each other because of Crookshanks and Scabbers all the more emotionally difficult to get through. Especially on top of her insane class schedule that year.
I also think Moaning Myrtle has a similar story up to a point, and it was only through lucky circumstances and Harry's kindness that Hermione didn't become the school's second weeping specter.
This was cross-posted from http://fayanora.dreamwidth.org/1228352.html
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