This is one that probably varies by hotel. I'm fairly certain that Marriott Reward's rules don't obligate the hotel to give her anything.

That said, my wife frequently goes ahead of me by a day or two for our trips to visit her family. She checks in to our Marriott with her as "Guest 2" and they've never *not* allowed her access to the lounge. (It's usually the same Marriott but we don't go often enough that people recognize her or anything.)

I don't think it's too rare that this happens...we've done it in a couple other places as well...nor do I think it's all that big of a bending of the rules. It's a little bending I suppose...but the fact that Marriott is welcoming of my wife is a bit of a competitive advantage for them over Starwood, which for the most part is not. (Hilton's better than both of them: she actually shares my status. When I hit a status tier, they mail us two cards - one with her name on it. She can book rooms as Guest 1 using my account and status.)