Soledad is correct. There are many scary hoaxes going around on the internet and you might be the victim of one of the hoaxes. It may be innocent on the part of your friend, because she heard it from someone else on on and on.

Go to this site: http://hoaxbusters.ciac.org

and there is a heading for scary hoaxes. There is one on the site about women and flat tires in the mall that is very similar to your story.

Sadly, you cannot always believe everything you hear. But it never hurts to be extra cautious.