Dear Henry,
thank you for your help. Her computer is located on the same internet setup, it is connected to the same Router. Her Anti-Virus Application is Antivirus Pro, same as is mine. But i'll try to deactivate it and reinstall the game, maybe this will solve the problem.
I hope my english is understandable, it has been a while since i hat my last practical experiences in writing/speaking english. But i hope i can improve myself during the time on this Forum. ^^
Edit: unfortunatley it did not work. Another issue with this computer is, that steam can only connect when using tcp protokoll and i have no idea why. Maybe this causes the Problem with Naval Action.