My own take on this. Hermione didn't have to go on the roof. She could've thought of a different method of taking Harry down. I forget if it has been specified, is there a time limit? They could've waited for harry to get tired walking about on the roof and picked him off later.

As such she is responsible for the risks she took going on the wall after Harry. Harry should have shown concern after her fall, but a full on apology does seem a bit thick.