Then you might say something like "That text you sent me turns out to be one of those Internet urban legends. Here's a link to Snopes.com that says it is not true: http://www.snopes.com/politics/crime/koch.asp."
Plus maybe something about how easy it is to be fooled by "Internet facts". She will probably be embarrassed that she sent the text to you.
That is exactly what I did do. I texted her the URL of the Snopes page which debunked the Koch stuff. Haven’t heard anything from her since. I’m thinking she is too embarrassed to text me back, since the Snopes webpage (which is run by LIBERALS) clearly said the rumor is FALSE.