sister relationship concern

Today I heard my sister talking on the phone with his boyfriend( which i'm not suppose to hear but i sleep in the same room)and she was saying that the only day she was happy from this week was wednesday because she was out of home, in school making a short film, and i got concern about it.

First of all it's because our family is very attached , it's not the type of family that you would always see complaining with each other. We like to do things together like going to watch a movie or eating at a restaurant or going to a theme park. And second, my sister didn't use to be like this before.

I actually have seen that in some of those activities she doesn't take part at all and she looks like bored. I think that it might be because she is growing up and thinking that she shouldn't be doing those activities with her parents at her age, other cause could be that she gets bored of being with her parents that are scolding her most of the time or\and she only is happy when she is with her friends and boyfriend. I know that this must be done by my sister but, How will I make her notice that?

For now I would keep up the same way to see what happens and I would do what you could tell me to do.