I’ve dealt with this with the infamous ding-dong trio at my barn. They have a gigantic portable “closet” that everything got ruined in because they left treats out. Their answer? Leave the treats out of their “closet”, but still out in the wide open, so EVERYone’s tack can get ruined!
Yeah, not happening.
I put 5 snap traps out near my stuff, and another 5 glue traps in and around their wide-open treat buckets (don’t worry, I check them daily and dispatch via shovel what is caught - I really don’t like glue traps, but don’t want the liability if someone else sticks their hand in a snap one). Lady squeals every time something is caught “Gosh I HATE seeing dead mice!” and moans and groans about “the person putting traps out”.
Seriously? What is wrong with some people? How can someone be so dumb that they don’t understand the cause and effect of this?
OP: I’d buy a tin for her. In addition, I would put steel wool in any opening in my locker to stop them coming in. Finally, I would put a single snap trap (get one of those newer black ones, they don’t hurt if you biff and it gets your hand or a cat paw) in my locker on the “mouse highway” so the first thing they see is yummy PB in the trap and WHACK no chance to go through my stuff - that’s if they can get past the steel wool you jam in the openings.
Also, your BO is not thinking. Lockers make it where the mice can do what they want, regardless of if the cats can get in the tack room. That is why I really don’t like lockers. If I were the BO, yall would have a little cat door cut in ASAP just to keep the pressure on in the area.
Totally unrelated aside - mice are cannibals and will often eat their comrade who met an untimely demise in the trap, leaving just the head for me to empty. G.R.O.S.S.