I'm thinking of withholding money from my sister
Why are you not giving your sister her money?
She has not paid me the money she owed me.
That's unfortunate she isn't holding up to her end of the deal... I hope you can try to reconcile so she learns how to pay you properly.
Okay, I'll tell her and hope she can change one day.
I'm glad to hear she has a chance of doing better for your sake. Hopefully she will honor her end appropriately.