Verified answer

That's one of her features. Maybe make friends with her and she'll go easier on you.

I don't know of a way to prevent it but, when the evil witch arrives at the lot you will notice she starts waving her wand then all of the sudden it will rain. When it rains it is raining vermin she just casted a spell... it is an automatic thing evil witches do just like good witches will create nice weather. Hope I helped!

That's what you get for having an evil witch on your lot all the time. Hence the term, EVIL. Next time she's on the lot, try building up your relationship with her. Or just don't have her over anymore.

Good luck!