Is a wife's conversation with non-mahrams—especially with her husband's friend who previously spoke ill of her honor, and in a manner that involves a type of flirtation—considered marital betrayal, or a normal matter given her upbringing?

A woman's conversation with a non-mahram man without necessity is a gateway to fitna (temptation/strife) and corruption, and the claim of brotherhood between them is false. The wife must obey her husband in refraining from this, and her disobedience is a sin. If the matter reaches the point of flirting, then this is dangerous. For the wife and her family to consider this matter normal is a deviation, and the husband must make clear to his wife the boundaries set by Allah. If she does not obey, he should employ means of reform with her, such as hajr (shunning) and non-brutal beating. If this does not work, then divorcing her is preferable. The man must uphold his right of qawamah (guardianship/maintainership) and prevent fitna in his home.