Okay, so I accessed a connection test through system settings, network settings and choosing to Test Xbox LIVE connection. However, these are the only results it gave me -

Network: Connected
Internet: Connected
Xbox LIVE: Connected

As you can see, it didn't tell me anything about my NAT. I know that it used to show it back on the old dashboard, but I don't know how to go about finding out on the new one. =/

Basically the problem occurs with a friend of mine who lives barely a mile away from me. It doesn't matter what game we try to play. If one of us is the lobby leader then the other is unable to join the game. The only way we're ever able to play together is when we get another person to create the lobby so we can both join, or if we both hop into a random public game. We can't get into a party chat if one of us is the leader, either. It wasn't much of a problem until she got RE5 which we wanted to play together, but we really can't because it's only 2 player co-op (excluding versus) so we're unable to connect to each other.

I don't know the first thing about system/router settings and have no idea how I can find out. Can anyone help me by telling me what the problem is and how I can fix it, or redirect me to a source of information that can give me the answers I need?