Playing devil's advocate here: say the crew allows the g/f to sleep and spend time in the roomette and they walk into the diner together. How exactly would the diner crew know she only has a coach ticket? Granted I've only traveled LD sleeper twice, but in both instances all I've had to do was write down my car and room numbers on the receipt. Nobody would really be cheating the system here because the sleeper charge covers meals for up to 2 people.
Mods: If this thought is out of line please delete.
Would hate to represent myself as a sleeper passenger and be caught eating a free meal, whether during or after the fact, if I could not produce a (e-)ticket stub displaying a qualifying class of service. If the powers that be receive two meal checks with the same room number, and match up the fact that only one person was ticketed in the room, it would be evident something's amiss.
Also, the printed manifest of sleeper passenger names is available to any crew member, so if they see two people (over the course of a two-night trip like EMY-CHI) eating meals for a one-person room, they just might put two and two together.