"Can't join" problem with a friend

I am trying to play with a friend on multiplayer but when we first tried the good old connection problem occurred. I also tried to connect to other games with the same result.

Through VPN i finally managed to join other lobbies but i still can't connect witg my friend in particular. She did the same things I did but the game just won't connect each other.

I read somewhere that i'm suppised to open some particular ports so i'll try that when i have time.

But why the hell does it let me connect to EVERY lobby except my friend's one (who can join every lobby as well)?

Edit: additional info: we both have the steam version, both playing asian dinasties

(Sorry for the english btw)