Jolie is the sort for discretion, when it's necessary. She is aware that Anna is more reserved than most, but with a boyfriend like Bro it seems strange that she'd be this oblivious. Regardless of that, Jolie doesn't think an adult relationship is anything they need to hide and she isn't the sort to cover someone else's ass when it isn't on the line.

So, she's just going to half turn in her seat and raise a brow at Bro, especially since he decided to be accusatory at her. She's willing to give him the benefit of the doubt here, but this is a dangerous question and he needs to nail the landing. The silence is probably more meaningful than any snark she could come up with.