Ah the misconception is back...
First, an accident, by definition, is something that happens in an unintentional manner...and unless Mitsuki was driving the truck that struck Haruka, then she had no hand in it. There are too many what-if's to account for for there to be a undeniable amount of proof to link Mitsuki to the fault of how Haruka was in the accident...for example, if Takayuki arrived on time, would they have left immediately or held a conversation? If they stayed in the same location, would they have been both in the accident, or would something have changed? There are plenty of questions to ask to counter the blame game
As for the whole 'friend backstab' thing, well, my opinions on this subject were made very clear elsewhere in this thread...suffice to say, the anime dropped the ball when it came to this part of the story.