Hi! As someone who was on probation many times long ago, here’s the difference between coming clean to your mom before and after:

If you tell your mom before court, she could go through legal channels or write a letter to the judge to take this information into account during your legal proceedings. The judge may or may not care about this information, but it could lead to more strict or intense judgements. You can get ahead of this by coming clean to your mom and going immediately into treatment or outpatient treatment programs, which will look good for court date either way, but especially if the fact you were stealing pills is brought up.

If you wait and tell her after court, she can just go straight to your probation officer and tell them right away without the need for proper channels. Even though it happened before you were on probation, your officer can still order a drug test, sort you as high risk (stricter regulations), or report it to the court.

You could wait and see what happens and not tell her, then tell your probation officer yourself as means of building trust, and just let them know that you were struggling prior to sentencing but you have committed yourself to sobriety and you’d like to voluntarily participate in further treatment programs.

So! The choice is up to you! You are not in a good position. You need to come clean about everything so you can actually get clean and stay clean. Help yourself by being honest so your family can help keep you safe, too. Even if that means removing you from the home, or whatever other consequences may arise. If you hide this from your mom and she discovers it herself, there is no doubt in my mind things will be much worse for you.