I'm going to insist my mom go no contact with someone I believe is toxic.
why do you want to keep your mom away from this person?
I think it's the only way to protect her from them.
While it is understandable that you want to protect your mom as best you can from others, you can't actually insist and make the decision to go no contact for her as that would be controlling and wrong. Rather than issue ultimatums to your mom, you should present your case and give her reasons why you think her relationship with that person is toxic and damaging. Your mother may or may not agree but you can rest assured that you tried your best to look out for her.
Wow, you're so sheltered. We live in the real world, not a fantasy bubble.
You cannot really make your mom do whatever you want. There are better ways to deal with the situation. As I said earlier you should have a conversation about it with your mom.