1. An investigative journalist made a best effort to try and talk to the accuser of the "13 year old rape" story. This was the conclusion:
2. The name "Katie Johnson" is apparently an admitted pseudonym.Quote
I don't know if Johnson wrote that letter. In fact, I don't know if the Katie Johnson I spoke to is the same girl who Trump allegedly raped in 1994, or if that girl even exists. I have never seen Johnson — in person, or via FaceTime, as I was originally promised — and I have not spoken to her only eyewitness, Tiffany Doe. To my knowledge, no journalist has.
3. A contrary account may be found here
4. If the account was credible, Clinton would have repeatedly referenced it in her campaign against Trump. She never did, which implies the charge was baseless.
5. In the USA, a person is assumed innocent until convicted in a court of law.
Anyone can believe anything. Feel free to accuse anyone of anything, believe the worst in anyone. It is your choice.