If You Comply to Take a Blood/drug Test for a Rehab Center, Will They Really Tell You Who Reported You?

I told a friend that I found alcohol bottles and my mom used to / has an alcoholism problem and I suspected a while ago that she did drugs. My friend reported it. Today, she got a call from a rehab center saying that, if she complies to a blood and drug test, they will give her a copy of the report and tell her who “anonymously” reported her to the rehab center. I guess my mom doesn’t have a problem after all because she laughed and decided to take the test (tomorrow) to see who reported her. I’m so scared; she’s going to be so mad at me– unbelievably mad at me– and there’s no way she would understand.

Will they REALLY tell her who reported her and give her a copy of what was said, or are the rehab people just telling her that to persuade her into it?
If you know, how do you know this? I just want to be sure…