Let's see how long your sister holds out before she asks you again for help of some type. You are being abused and should refuse to assist her because you are working at your own job and preparing for your own future. That should teach her a lesson she will never forget.

Stop the abuse with this most recent incident and see that it doesn't continue to
happen.

You deserve a much better living arrangement than the one you have.

Take care of yourself first; that will enable you to benefit your loved ones without having to endure the (sorry to say this) arrogance and stupidity of your sister.