It seems to me that what's done is done, and there's no point in making a martyr of yourself when it won't help another. Everyone is the wiser.
From the tone of all this, it sounds like Bijnas and Silly Girl are still communicating- that's good. Shit happens, and friends get each other THROUGH it even if they can't get each other OUT of it. If she misses classes because of court dates, hey, go pick up her assignments for her. Look out for her while she is otherwise occupied, the way you asked her to look out for you while you were away. That would be a reasonable thing to do.

Actually- there's an analogy.
Silly Girl misses class for xxx avoidable reason.
Silly Girl asks Bijnas to pick up assignment.
Bijnas gives her the wrong assignment through some stupidity or carelessness.
Silly Girl turns in a paper that gets an F because it wasn't the right one.
Whose fault was it that she failed? It was a dumb move on his part to give her the wrong assignment, but she should have been in class herself. They can now play the blame game until graduation. Or they can say, oh crap, we both fucked up, good thing we are still friends.

Bijnas, I sentence you to wear a hair shirt (monk fashion c. 900AD) until your friend is off probation. Self-flagellation optional.