Will I get deported if I'm a legal resident but I got caught with $83 in merchandise?

The first thing you must right away is to hire a good immigration attorney. They are experts who alien foreign criminal defendants and their criminal defense attorneys about the adverse immigration consequences of criminal convictions. The immigration attorney will help and advise your criminal defense lawyer about the immigration aspects of the various charges you are dealing with. Clearly, a not guilty verdict is best, but where that is not possible, you may have to cop a plea. The immigration lawyer will help your criminal lawyer help to structure a "safe harbor plea". Safe harbor plea is one that will not cause you to be deported. You should not assume that your first conviction was sealed and so, it is even more important you are not convicted for another offense which will worsen your situation. Go find and talk to an immigration expert right away before accepting any plea

What is your birthday? When did you become a permanent resident? When did your mother become a naturalized citizen?

Theft is a crime of moral turpitude; and being convicted of a theft will likely put you in removal proceedings (if ICE does not come for you right away, the removal proceedings will be initiated when you apply for citizenship or for renewal of your green card). For this reason, if it isn't too late yet, get a good criminal defense attorney and ask him to plea-bargain your offense to something like disorderly conduct, if possible. Regardless of the outcome of your criminal case, it would be a good idea to find asap an immigration attorney who would be familiar with your case and be ready to intervene if you find yourself in removal proceedings. It is particularly important if your previous conviction has any immigration law consequences (most criminal convictions do; and it does not matter that yours was sealed). For instance, if you have only one conviction for a crime of moral turpitude, it might fall under the "petty offense" exception to the deportation statute; but, if your sealed conviction was for a crime of moral turpitude, too, it is going to make your deportation much more likely. In some cases, it might be possible to reopen and vacate (wipe out) the prior conviction, but it takes time, and the Immigration Court will not halt removal proceedings to let you complete that process; so, the sooner your attorney would start working on it, the higher your chances not to be deported are likely to be.