Re: They cheated on the exam and it’s just not fair… should I tell prof?
If the person in question had stolen paper tests from the professor, or if she has hacked his computer to steal confidential information, then it would have been a different story.
But in this case telling on her is mere snitching.
Asking other students what questions they got on the test is not illegal. I wonder in what sort of institute OP studies. But it is the responsibility of the college/university to test everyone at the same time, so that nobody can copy any answers and pass it forwards.
Even if someone gets ill, the test is never resheduled. The person gets a chance to catch it up during resits. And if you mess up again, then bad for you. Try again next year.
So the it’s a failure on the part of the professor and the college or whatever it is.