^^^ditto all that
Spraying the fly mask is overkill.
You also run the risk of the eyes having an allergic reaction from such close exposure to the fly spray.
As an example, we can't smell environmental allergens but they don't have any trouble puffing up the eyes of folks sensitive to them
The healthiest thing you can do is to keep the fly masks clean.
I put all of mine in the washer every night, on slow cycle for four minutes, with about 1 TBS of laundry soap. You don't want to use a lot of soap, elst it won't come out of the masks; it doesn't take much to get them clean
You could buy Gracie a couple fly masks, so you would only have to run them thru the washer every couple days