Hi Suman,
If you have observed that she tends to notice or make eye contact with both guys and girls, she may be a people watcher by nature.
People watchers tend to observe other people in order to figure out what their story is.
Perhaps she didn’t show this side of her personality until recently because she only recently felt comfortable enough with you to do so, being that the both of you have now been in a relationship for four years.
Try not to get panicked enough at what you have noticed that you start acting negatively towards her as though she has already cheated.
This may cause friction to the relationship that could lead to unnecessary arguments.
Just focus on never taking your relationship with her for granted.
This is where you need to make sure that you are continuously engaging in new activities with her and consistently acknowledging her as someone that is special to you.