Which is worse - insult or breach of privacy?

Person A writes an email to an old friend who does not know Person B. In that email, Person A says Person B’s daughter is “snotty.”

Later, Person B has an opportunity to read Person A’s email without Person A knowing. Although Person B says she should not have read it, she did.

There is hurt and anger in this situation. Who, if anyone, should be more upset – the person who found out her daughter was called “snotty” or the person who had her private email read? Is ending a friendship over either one justified or an overreaction?

There are a lot of details that could sway people toward one side or the other, but I just want a base line answer to feel like my feet are back on the ground. This entire situation has spun out of control.