I am babysitting this girl, and I really don't want to get strep since she has it. How can I avoid it?

Stay Away. 24-48 hrs of antibiotics seem to elimate the contagious phase. Otherwise avoidance is the best policy.
Good hygeine. Avoid contact of your hands with your mouth and face, do not eat or drink after the person, wipe down surfaces with soap and water or disinfectants as allowed and keep your fingers out of your mouth. Try to avoid mouth contact with the other person such as kissing or licking and any objects they may have touched (toys). Avoid exposure to sneezes, etc. It is by contact that you contract strep.