Think about it like this. We watch porn right? We have watched a lot of porn since our childhood. But do we try to do those things? We go for MILFs? Do we do gangbangs? Yeah we have kinky fantasies. But they are not the reality right? Relationships are different. I think it's same for girls.
It's normal having insecurities. But fuck them. If they want to watch they watch. Of course they will have some fantasies in their mind just like us. But it's ok. Be mature to accept them. Talk about them openly with her if you can.