Well I don’t have ‘explosives’ knowledge...but I do have ‘hair’ knowledge and, just a guess here, that if she was using peroxide its NOT the type you get in the drug store (which is less than 1% solution). Professional ‘grade’ is 8 to 10 percent; but can go as high as 40 (for very coarse, dark hair lightening—put it absolutely would fry the hair).
My guess, that she had MORE in her car (as a stylist) (hair spray; gel; acrylics for nails; etc.) and that the collective assemblage of products caused the fire (started by the cigarette).
the 10-40 volume peroxide you are talking about is roughly a 6% solution.
And now that I think about (been a long time since I went to beauty school and I don’t keep up since I developed a sever allergy to the chemicals)the powder bleach that is mixed with the peroxide could start a fire if it came into contact
with transmission fluid.
Lots of fires start in peoples sheds where they store their transmission fluid above their pool chemicals when the bottles leak.