Most seem to think a management problem instead of a tenant problem.
Management problem if there are unsealed openings into the apartment. Where they can get in. But still have to be attracted to a food source. Windows or doors that dont close. Has to be a large gap for flies to get in.
But a large number like she said invasion. Has to be attracted to the apt or come from someplace. Which is from some rotting garbage or food in the apartment. First maggots then they turn into flies. Unless she let them in with doors or windows open.
Cant see how mgt can control that.
All dumpster areas will have flies especially in warm weather. Tenants put rotting food in bags that are not sealed. And they dont make air tight dumpsters anyway.
Cleaning a dumpster area would help but only some. And temporary. Since tenants will come there the next day.
I think she seen improvement because whatever food that rotted had been eaten. No type of spray is going to help much with flies. You would have to spray every surface in apt. And even them EPA does not allow them to make anything that strong anymore.
I think she would have had the same luck chasing them around and trying to hit them with the bottle.
If you want something sort of fun that works. I keep one on my deck.
https://www.ebay.com/itm/BUG-WARRIOR...72.m2749.l2649
These actually have power and work. The other ones on amazon I have tried are more like kids toys.
And of course you still have the old plug in bug zappers made for outdoors. Just use inside, they do work.
Every backyard had one back in the 80's when they came out. Then they found out they did kill a lot of bugs. But they also attracted many more to your yard.