If her windscreen was tinted it was a legitimate stop. However, she was legally entitled to remain within the vehicle. But, by asserting that right she got the copper's back up, so he claimed that was grounds to suspect her of something (though, at that stage, he didn't say what), as grounds for a search. This almost certainly wasn't lawful; choosing not to comply with a police officer's request (which has no legal weight) isn't a reasonable ground to suspect someone of a crime. As such, she was entitled to resist the search, such that the subsequent arrest (apparantly for obstruction) would've been unlawful, too. This is a good example of what
Bahnhof Strasse and I were discussing recently; the fact that you may not be obliged to comply with the police, but that it's sometimes less hassle to do so.