The former world number one will now face last year's Wimbledon finalist Jasmine Paolini in the semis on Friday, the Italian progressing with a 7-5, 7-5 defeat of Beatriz Haddad Maia.
For Swiatek, 24, this is her second appearance in a grass-court semi-final, the first coming at Bad Homburg two years ago.
For the Polish winner of the French Open in 2020, 2022-24 and US Open in 2022 this is her first tournament on grass of the season, with Wimbledon starting on Monday.
Swiatek, beaten in the last four at Roland Garros three weeks ago, made it to the last eight at Wimbledon in 2023, her best result at the third Grand Slam of the year.
Friday's other semi-final in Germany will be between top seed Jessica Pegula or Emma Navarro and Mirra Andreeva or Linda Noskova.