Fröhlich, 29, spent the first part of the EuroLeague Women season with Broker Kosice and averaged 13 points and nine rebounds in six games.
The veteran power forward's move strengthens the Gambrinus line-up ahead of their forthcoming play-off showdown with Bourges Basket.
"The offer from the club, one of the best teams in the last 10 years, was appealing," Fröhlich said.
"It is a new motivation for me and I would like to help them reach the EuroLeague Women quarter-finals."
Fröhlich returned a positive test for the banned substance Hydrochlorothiazide in late 2008 but was recently cleared to play basketball again by the FIBA Disciplinary Panel.
Gambrinus hosted last year's EuroLeague Women Final Four and finished runners-up to Spartak Moscow Region.
The Slovakian press had reported last week that Kosice had wanted to keep Fröhlich but were unable to match the offer Gambrinus were making to the player.
Kosice, meanwhile, have bolstered their line-up with the addition of Lithuanian center Iveta Salkauskeová.
