The 25-year-old previously played for FCR 2001 Duisburg, TSG 1899 Hoffenheim, Frankfurt and Verona Calcio prior to her spell with the Black Cats.
“I am thrilled to be joining Liverpool Ladies and I’m really looking forward to meeting my new teammates,” said Preuss.
“This was a fantastic opportunity for me and one that I could not turn down. The club has real ambitions for the future and I am confident that I can develop my game whilst at the club.
“I really enjoyed my time with Sunderland Ladies but this now presents me with a new, exciting challenge which I’m really looking forward to.