This is so crazy

My cousin and her husband have been together since they were 15.. they have 2 beautiful kids... a 7 year old and their rainbow baby girl, who is 14 months old. Her name is ELLA. My sweet cousin, who is 34 had infertility problems and so badly wanted another baby and was over the moon when she found put she was pregnant with their baby girl. Since she chose the name of their 7 year old, it was her husbands turn to pick the name for their daughter. When he chose the name ELLA, she fell in love. Fast forward to a few days ago, my cousin and her husband got into a fight because he was drunk. When he was passed out, his phone kept going off so she decided to look at it. The name of the girl, who was texting him was ELLA in his phone. She called the girl and found out that her name really was Ella and that she and her husband had been having sex for almost TWO years together!!! He named their baby after the girl that he was having an affair with!!!!!!! To make matters even worse the girl is 19 years old!!! My heart aches for my cousin. What would you do if you were in that situation? My cousin wants to rename her daughter, but wonders if that's wrong to do