How will he know she's working elsewhere?
Even if she's caught, they aren't going to deport her. She'll either get a "cease and desist" letter and/or a meeting with an immigration counsellor, but she won't get deported.
Have her get another job, show her texts to this asshole's superior and get him fired. If he wants revenge, what's he going to say? "Uh hi, Canadian immigration, there's this girl I know who is working illegally. I don't know where, exactly, or for whom...but trust me on this". Believe me, they have much better things to do.