My girlfriend rarely makes eye contact with me during conversation?

I have noticed whenever I am in her house that if there is 3 or more of us in a room all having a conversation she makes constant eye contact with her family especially her Mother but even though I'm involved directly she constantly looks at her and not me This has been happening for years we have a very good relationship but it is frustrating me I have mentioned it in the past but it turns to a fight. Is this a sign of something?