I wouldn't encourage the idea. If you read the label on virtually any pesticide, you will see this statement.
"It is a violation of Federal Law to use this product in a manner inconsistent with its labeling"
I'm sure the Feds probably wouldn't go after your mom if she sprayed a bad guy with wasp spray, but that's not wasp spray's intended purpose and it could create civil liability problems if the bad guy were permanently blinded. I'd stick with the pepper spray or buy a gun.