I'd guess zero. They run pretty much straight water, so any spills on the track from overheating or wrecks evaporates quickly and won't be slippery from residual glycol.
I posted a link above about land racers banning antifreeze due to flammability concerns.
And up beyond that, a link to problems with glycol mists in fire suppression systems.
Still very unlikely in this case, but water-glycol mists can ignite.
Something else happened here- it might even be that she was unconscious when the whole thing started since there was very little evidence of fire in the cockpit of the BMW.