Case 1: Sally can play with Bob & Tony as a guest. In the example of Halo 3, Sally cannot use her own profile, and if Tony's profile is HiI'mTony, she'd appear as HiI'mTony(1).
This allows all three people to play in Social playlists, that allow guests.
(In fact, one Gold member can sign in up to 3 others on the same xbox for a four-man team over social matches on Live ^^b)
Case 2: Sally can get a Gold Account anndddd play on the same box as Tony. She can now use her own profile, has chat rights, and can track stats/play over live. Sally & Tony can play together in Ranked matches (with Bob if they wish) in playlists that have a max party size that is greater than one, i.e. Team Slayers. They cannot play together in ranked matches that are solo, like Lone Wolves (due to its max party size of one

).
Case 3: Make the biatch get her own damn TV and stop clogging up yours for splitscreen. That would obviously require another Xbox and her own Gold account on that box.
Did that help at all Cmdr?
You're welcome.
-Tae
(Sorry I didn't notice this eariler...)