Is a wife's going with her friend and her friend's husband in his car considered unlawful seclusion (khalwa), and what is the evidence for that from the Qur'an and Sunnah?

A woman riding in a car with her friend and her friend's husband does not constitute khalwa (unlawful seclusion). However, a woman must obey her husband in matters of righteousness. So, if he forbids her from going out or riding with a non-mahram man (a man she could lawfully marry), she must obey him. This obedience is particularly emphasized here because it protects his honor. If the wife insists on disobeying, she is considered nashiz (rebellious) and may be dealt with according to the rulings for a rebellious wife.