TN visa requires a legitimate employer-employee relationship. If she is a co-founder of the company, which she has advertised herself as being, then the TN visa is illegal. Add on the fact she tried 3 times in various borders is more than enough evidence to detain her for immigration fraud.

Do I think it's right? No.

But is it lawful? 100% yes. I've seen draconian behavior at the border so I'm completely familiar with how things are so I'm not surprised.