I swish water in my mouth when my mom comes over so I don't say something nasty to her
That's really odd. Do you want to make sure you dont hurt her?
I don't want to say anything nasty to her.
Its great that you are doing your best to be kind to your family. Using mouthwash in this situation however does not seem like it would be that much of a benefit.
I think it is better than nothing.
At least you are doing something. You need to try to hold these bad thoughts in when your family is around.