1) The Hydrogen Peroxide ignites in a massive ball of flames which is seen for miles and which results in instant death for the young woman. (This seems implausible.
2) The smoker is startled by the sudden experience of some flames coming from her back seat. As she turns around to deal with these pesky flames, she drives into an oak tree, resulting in her death.
One never knows.
re: your number 2:
If, and I still have some issue with this story....
In a hot, sunny car interior, the peroxide may have decomposed in the back seat, releasing free oxygen and creating an oxygen-rich environment inside the car. Then the tip of the ciggie flared up. H2O2 will not decompose to anything flammable, but as we all know, excess oxygen impinging upon an already-ignited something will cause a flare-up of some kind.
Just being a little nitpicky on ya. Same overall result you cited.
Interesting comparison case here http://www.ntsb.gov/publictn/2000/HZB0001.htm involving a spill of 2 gallons of 35% hydrogen peroxide in an aircraft cargo hold. After landing, some soaked items nearby were tranferred to another aircraft, and later found smoldering when that aircraft landed. No explosions, despite the fact that large quantities of this stuff, after time for plenty of evaporation-concentration, were lying around airport tarmac while all sorts of activities (including combustion-engine powered vehicles) went on right next to it.