I'm sorry to hear that you have tried to get her without any success. If you look through this site, there are many successes from her. I would try writing to her again now and supply your own picture and SASE!! Seems that she's not as busy as she was before.
her autographs are 100% authentic, this is from her offical website:
There are a lot of shady people who want to make money with forgery. More and more I discover photo fakes of me in the world wide web and also more often so-called Heidi Klum signatures. I am really mad about these autograph fakes because unsuspecting fans sometimes buy them for a lot of money or get them at an internet auction.
I was looking for more transparency and security for my fans. At the end something concrete came out: a special kind of signet identifying all my autographs as originals from now on. I put this button of genuineness right on my signature to make fans sure that this autograph is really mine.
The badge is round and transparent showing my Heidi Klum logo in black and red. It’s manufactured by a german factory in Kreuztal. The process is very special and costly because a synthetic foil, being printed with my logo, is covered with casting resin to become “sphericalâ€Â. So at least the signet sticks on the autograph like a raised big button.
From now on it’s fact: You find my original signature just there where the button of genuineness sticks on.