H'okay, so nobody had any input but I'll post an update anyway in case the people of the future search the board for this kind of thing.
I asked The Vet about the grass and he said she probably just enjoyed it, like catnip. He also said the whole "Cats eat grass to throw up" thing was just a theory and he didn't actually believe it was correct. As long as she was eating fine and looking generally healthy, he didn't think there was anything to worry about.
So, she's just a little wierdo then.
(He also said that when he gets reincarnated, he wants it to be as my cat so I clearly give the impression of somebody who knows what they're doing with regards to feline welfare).