Regardless of what kind of tin you buy your locker partner, you must bring the general mouse problem up with management because the solutions have to be implemented in the whole barn. Mice travel.mice replicate. Mice are destructive and spread disease. They can’t be eliminated but there can be controlled a bit.
In my barn the mice thrive off the seed heads of the Timothy hay in the lofts. It’s one thing to lock up all your brain but you can’t lock up all the hay! They got out of control this past summer until we changed exterminators.
So nice can live off the hayseed and nest in your blanket box and pee and poop on everything.
As far as your locker mate thinking you are overstepping, how do you know? She night be silently rolling her eyes every time she sees you sweeping. You just don’t know.