Ignorance is indeed bliss!
On the other hand, Rebecca was also not doing very well. She was sad and depressed because of the news that Joseph was not her actual father, but she was experiencing utter guilt. Rebecca felt that ignorance, in this case, was indeed a blessing and that’s she should not have even taken the DNA test in the first place.
According to what Joe claimed, Rebecca was dealing with significant emotional distress and confusion regarding her own identity, which was an obvious case. She dealt with emotional impairment, disorder, and tons of guilty feelings. She was also dealing with the disappointment that she did not get to be a child of her parents genetically.