My cousin is the same way, but nobody in the family takes it badly. She has her friends (she's a dancer, and so are they) and she talks and they make parties and she's a blast. In family gatherings, there's no much to talk about and so she acts accordingly. LW is an arse, and aside from that probably a bore like my family. DIL probably doesn't even dislike her in laws (though she should), perhaps she just thinks she's being polite.