My fiancé is an Indian National with a German student resident permit with more than a year of validity. Can she stay in the Netherlands, let's say for over 3 months (with her address still registered in Germany) ?
I read that you can travel outside Germany(within Schengen zone) for up-to 90 days. Also, how do they even track these activities? because there is no border control check while travelling by train or even flight from Germany to Netherlands.