In a way it was House's fault because he went drinking Amber came for him, instead he left for the bus and forgot his cane in the bar. Amber then gets on the bus to give House his cane. Amber was on the bus when it crashed and it damaged her kidneys. Amber wasn't allergic, her kidneys weren't filtering it out of her body and since the medication wasn't filtering it poisoned her. The medication bonds to protein so dialasis wouldn't filter it out either making her die from the poisoning of the medication. If she wasn't on the bus she would have lived her kidneys would have filtered the meds out and she would have lived on no worries and her flu gone but she was on the bus and that was because of House.

Please someone correct me if I am wrong but I'm pretty sure it is right.

Just rewatched it and I am right.