The 9th arrondissement is not a neighborhood that allows running.
The main axes like the Grands Boulevards will be full of obstacles, walkers, people who go to work, cafe terraces, intersections every 100 meters with traffic lights. Less busy streets will not be better with their narrow sidewalks, people walking, crossroads. This environment is not made for training and your friend may disturb other people.
The closest place would be to go to the quays of the Seine right bank (north bank) through the Jardin des Tuileries.
The entire route along the banks between Place de la Concorde and Bastille is dedicated to this kind of activity. (it's necessary to go down on the bank)