That's crazy. It sounds like a story from that animal planet show "Lost Tapes." You should send the story in, maybe you will get a episode done for the show.
And to all the people who say there's no proof that he does exists, what proof says he doesn't exist? They just came across an animal they thought to be extinct. From 1939 to 2002 nobody had seen one.
http://www.wired.com/wiredscience/2010/07/horton-plains-slender-loris-lives/
They just recently got a picture of it. If Bigfoot doesn't exist he knows where to hide because there are parts of swamplands that nobody goes, and weird fucking shit people find like the woman and her cow story told by the OP.
Bigfoot exists and one day someone will headshot that beast.