The captain of the Sea-Watch 3 ship is expected to be questioned in the southern Sicilian town of Agrigento on Thursday morning.
Rackete was arrested on June 29 for entering Italy's Lampedusa port despite a veto imposed by far-right Interior Minister Matteo Salvini, and knocking a coast guard boat out of the way to land 40 migrants after spending more than two weeks blocked at sea.
A judge overturned the arrest three days later, saying the 31-year old had merely acted to save lives.
But the Sea-Watch 3 remains in police custody in the Sicilian port of Licata and Rackete is still the subject of two investigations – one for entering Italian waters despite a direct order to stop, and another for aiding illegal immigration.
Supporters of Itaian right-wing parties in Rome hold a banner reading “Other than 'Liberte, Egalite, Fraternite': exploit the Africans, pay the slave traders. Shame!” Photo: AFP
Rackete will be heard on the latter on Thursday, and will have to explain why her crew rescued the migrants without waiting for the Libyan coastguard, which has jurisdiction over the stretch of water in which they were found.
The 31-year-old will also be asked why she then sailed the Dutch-flagged vessel to Italy rather than a Libyan or Tunisian port.
Salvini insists that Italy's ports remain closed to people who attempt the perilous Mediterranean crossing.
Prosecutors in Agrigento appealed to Italy's highest court this week against the decision to drop charges against Rackete for forcibly entering the port of Lampedusa, in the hope of establishing a precedent to put off other privately run ships.
A few days after the Sea-Watch drama, another charity vessel forcibly landed in Lampedusa, a scenario that is likely to recur.
Salvini's hardline stance has led to an upsurge in investigations into charity rescue vessels.
In March 2017, the Spanish vessel Open Arms was seized and its captain and head of mission were prosecuted after the crew refused to hand saved migrants over to the Libyan coastguard, which arrived at the scene during a rescue operation.
A month later a judge ordered the vessel be released on the grounds that crisis-hit Libya could not be considered a safe port.
And the prosecutor's office in Catania, eastern Sicily, recently archived the case against the captain and mission head.
The same prosecutor closed a similar probe against the NGO Sea-Watch after a rescue operation in January, concluding that the crew's actions were justified.
But the Sea-Watch 3's dramatic port entry in June marked a new chapter in the war between Salvini and charity vessels.
The arrest of Rackete sparked an online campaign which raised over 1.4 million euros in a few days to pay her legal fees and enable the German NGO to continue its operations, with a new boat if necessary.
On Tuesday the parliament of Catalonia in Spain voted unanimously to honour Rackete with a Gold Medal, its highest award.
And the city of Paris announced a donation of 100,000 euros to Sea-Watch, as well as a medal for Rackete and Pia Klemp, another German captain prosecuted in Italy.
Paris's move infuriated Italy's far right, which noted that the French government had remained silent throughout the 15 days the ship had been blocked at sea, despite Rackete's numerous appeals for a safe port.
Salvini has stepped up his attacks on the rescue charities, which he has accused of aiding people-smugglers, while calling Rackete a “bigmouth” and a “criminal”.
Rackete filed a complaint last week for defamation and incitement to violence, noting that Salvini's hostile messages on social networks have prompted an outpouring of sexist, violent and threatening comments from users.