I stole my mother's credit cards and wrote a check on her account. Can she press charges if I am only 17 and a family member?

Yes you can be arrested. If she chooses to press charges you will be treated like any other criminal. The fact that you are a relative is irrelevant.

Illegal conduct of defrauding your mother that you describe has very few, if any, valid defenses. You should immediately stop this criminal misconduct. If your mother decides to take the matter to the police, I agree with the answer above that your status as a family member provides you no defense.

If your mother does press charges you can be convicted to serve a sentence or other penalty for the crimes you have admitted to have done. Your mother has a written record of the credit card charges you made on her credit cards because the credit card company keeps those records. You will not get away with the crimes.