Was it the right decision to make?

My friend's ex and the father of her daughter is letting her down all the time. She had the little girl with this guy by mistake. Lets say, she was cheating her husband. The husband subsequently was involved in motor accident and died. My friend didn't want the biological father to know about the paternity of the child. Following her husband's death, we felt it was unfair for her to deny her daughter of her right to know and meet her father. They met. Since then, the father has not being paying much attention to his daughter. This hurts my friend so much. She regret to have disclosed the truth. She also has a problem having her died husband's family funding out the truth. They will be hurt.