Is my sister depressed or being affected by the street drugs she takes?

The answer to your question is that the drugs are affecting her personality and altering it a lot. Drugs make people have mood swings they are altering the chemicals in your brain and they can make you angry as well. She needs to go to therapy and dig deep to find out what is causing her all of this misery that she is using drugs to get rid of. She needs to really get off of the drugs or they will ruin her life, i would suggest you or someone in your family bringing her to a rehab she needs help immediately.