According to the article:
A German woman who converted to Islam has been placed under surveillance after police thwarted an attempt by her to travel to Iraq as a suicide bomber, media reports said.Note that neither Sonja B. nor her two co-conspirators have been arrested. In fact, it appears that only Sonja B. was "placed under surveillance"; the article never says what happened to the other two women.
The 40-year-old, identified only as Sonja B., is one of three German women said to have used the internet to disclose their intention to carry out missions against US soldiers.
Police reportedly prevented them leaving Germany in April.
I'm not sure what an aspiring German Jihadi would have to do to get arrested, but Germany has already proven its lack of will in fighting terrorism.