No - she could grab a card and have someone forge his writing. Only way to prove it is for her to release mobile phone text messages or something from Herman that can't be disputed. I doubt she has that. What she has is a trail of a lot of calls to/from Herman. While it doesn't prove anything it doesn't look good for Cain. Defending himself against 5 women is not a good place for Cain to be.
That is the bottom line. Better to come out now than to implode after he gets the nomination.