Have a look at Section 5 of this MSDS
http://www.havoline.com/images/products/pdfs/anti_exlife.pdf
This material will burn although it is not easily ignited.
Not classified by OSHA as flammable or combustible
Is that the kind of antifreeze she used? Some kinds of BMW antifreeze don’t contain any water at all, although they recommend 50/50 blend with distilled water for many types.
It sounds very odd.