It depends. If she only added you as an authorized user then it will affect your credit in no way. The only thing this will allow you to do is to legally use the credit card. The bill will still come in her name, and the account history and payments will be tied to her name and social security number. You have most likely received the high limit because of your mother's credit score.
Use the card responsibility and make payments to your mom for anything you buy monthly. While this will not help your credit score, it will get you into a pattern of responsible payments and hopefully keep you from charging (and living) beyond your means.