Accepting no answers

We have our up days and down days with TSG. Our up moments, our down moments, moments when we feel we are doing this and making progress and times when we feel like throwing in the towel. How can I help my 13 year old and 15 year old accept “no” answers even if we may have made a mistake? My daughter asked to spend an hour with a friend after track. We weighed what we knew at the time and decided she should come home since she had an early morning. She has been condescending and argumentative ever since this happened and is angry, frustrated and mean. I tried calmly explaining that she was not accepting a “no” answer and she started in trying every way she could to get me to lose my cool. Finally on her 4th attempt to wear me down, I snapped. I was nursing our 1 year old and putting him down to bed when she came in arguing. Then my 15 year old wanted to shower and we said he needed to shower in the morning. Both of them did not disagree appropriately either. Help. How do we teach this skill more effectively of accepting a no answer?