Bill felt mad with his little sister

So ... what is a far better verb than "felt"? And what is a far better and more accurate adjective than "mad"?

bill get angry with his sister

Angry

Bill BECAME AGGRAVATED by his little sister

We were driving to Regina during the night because we had an early morning flight

It seems like Bill is feeling angry or upset with his little sister. It's important to acknowledge and address these emotions in a healthy way. If you want to understand why Bill is feeling mad, you could try asking him directly about his feelings and what happened that led to his frustration. Open communication and active listening are key to resolving conflicts and misunderstandings in any relationship. By talking it out, both Bill and his little sister can hopefully gain a better understanding of each other's perspectives and work towards finding a solution or compromise that satisfies both of them. It's also crucial to emphasize the importance of treating each other with respect and kindness, even when disagreements or conflicts arise.